---
title: "Injection molding machine troubleshooting"
url: "https://www.imspares.com/troubleshooting/"
---

# Injection molding machine troubleshooting

Symptoms grouped by where they show up. For each, the likely causes are listed with the most likely or easiest to check first.

## Problems with the molded parts

Defects in the molded parts that often trace back to a worn or faulty part of the machine.

### Short shots: the part is not completely filled

On a mold that used to fill, a short shot usually means material is not reaching the screw, melt is leaking back past the check ring, or injection is weak. Check the hopper first, then watch the cushion: one that varies from shot to shot or runs to zero points to the check ring.

URL: https://www.imspares.com/troubleshooting/#short-shots

1. **Material is not reaching the screw**: Check that the hopper has material, the slide gate is open and the pellets are not bridging in the feed throat. A throat that runs hot because its cooling water is off, low or blocked by scale makes the pellets bridge. ([Hopper and feed throat guide](https://www.imspares.com/injection-molding-machine-parts/barrel-screw/hopper-and-feed-throat/), [Short shots article](https://www.imspares.com/blog/short-shots-injection-molding-causes-fixes/))
2. **Worn or damaged check ring**: A cushion that varies from shot to shot or runs to zero, or a screw that creeps forward during hold, points to a leaking ring. Inspect the ring, seat and tip with the barrel at processing temperature and purged empty, wearing heat-resistant gloves and a face shield. ([Check ring guide](https://www.imspares.com/injection-molding-machine-parts/barrel-screw/check-ring/), [Screw head wrench](https://www.imspares.com/parts/mc-gmp-01/))
3. **Blocked nozzle or nozzle filter**: Injection pressure that rises at the same speed setting, or a high injection pressure alarm, points to a restriction. Retract the carriage, remove the nozzle while it is still hot and clean it with brass tools, and clean the filter insert if one is fitted. ([Nozzle problems article](https://www.imspares.com/blog/injection-nozzle-problems-troubleshooting/), [Nozzle filter guide](https://www.imspares.com/injection-molding-machine-parts/barrel-screw/nozzle-filter/), [Injection nozzle](https://www.imspares.com/parts/mc-bc-07/))
4. **A barrel zone running cold**: Look on the temperature screen for a zone below its set point while its output is high. A clamp meter on the band's cable shows whether the band draws current. ([Barrel temperature zones guide](https://www.imspares.com/injection-molding-machine-parts/heaters/barrel-temperature-zones/), [Ceramic heater band](https://www.imspares.com/parts/ec-ht-01/))
5. **Weak injection from the hydraulics**: If injection speed and pressure are both lower than expected, check the oil level and filter, then measure the pressure at the pump outlet with a calibrated gauge. Worn injection cylinder seals give the same symptom. ([Hydraulic pressure loss article](https://www.imspares.com/blog/troubleshooting-hydraulic-pressure-loss/), [Injection cylinder guide](https://www.imspares.com/injection-molding-machine-parts/injection-unit/injection-cylinder/))

### Flash: thin plastic at the parting line or around the pins

Flash on a mold that used to run clean usually means the clamping force has dropped or is not spread evenly across the mold. Check the actual clamping force before blaming the mold.

URL: https://www.imspares.com/troubleshooting/#flash

1. **Clamping force too low or drifted**: On a toggle machine the force is set by the mold height adjustment, and it changes as the mold temperature changes. Check the actual force once the mold is at working temperature. ([Clamping force guide](https://www.imspares.com/injection-molding-machine-parts/toggle/clamping-force/), [Mold height adjustment guide](https://www.imspares.com/injection-molding-machine-parts/tie-bars/mold-height-adjustment/))
2. **Hold pressure set too high**: Too much injection or hold pressure can push melt past the parting line even when the clamping force is right. Review both pressures before changing the clamp. ([Sink marks article](https://www.imspares.com/blog/sink-marks-injection-molding-causes-solutions/))
3. **Worn toggle pins and bushings**: Wear in the toggle joints lowers the clamping force at the same setting. With the clamp depressurized, measure the play at each joint with a dial indicator. ([Toggle bushings guide](https://www.imspares.com/injection-molding-machine-parts/toggle/toggle-bushings/), [Toggle link bushing](https://www.imspares.com/parts/mc-tl-05/), [Toggle pin](https://www.imspares.com/parts/mc-tl-03/))
4. **Uneven clamping: flash on one side or one corner**: Flash in one place points to platens out of parallel, a tie bar nut that has turned or worn tie bar bushings. Measure platen parallelism before replacing parts. ([Platen parallelism guide](https://www.imspares.com/injection-molding-machine-parts/platens/platen-parallelism/), [Tie bars guide](https://www.imspares.com/injection-molding-machine-parts/tie-bars/))
5. **Worn ejector pins or pin holes**: Flash around the pins comes from too much clearance between worn pins and their holes, or from injection and hold pressures that are too high. Pin repair is mold work for the toolroom or the mold maker. ([Ejector pins guide](https://www.imspares.com/injection-molding-machine-parts/ejector/ejector-pins/))

### Sink marks: dents in the surface over thick sections

Sink marks are mainly a part design and process problem, controlled by hold pressure, hold time and mold temperature. If they come and go from shot to shot on an older machine, check that the machine holds the pressure consistently.

URL: https://www.imspares.com/troubleshooting/#sink-marks

1. **Hold pressure or hold time too low**: Hold pressure and hold time are the main process controls for sink marks. If the gate freezes before the thick section has cooled, more pressure will not reach it. ([Sink marks article](https://www.imspares.com/blog/sink-marks-injection-molding-causes-solutions/))
2. **Worn check ring**: A leaking check ring lets melt flow back along the screw during hold, so the pressure on the part varies. Watch the cushion during hold: if it varies or the screw creeps forward, inspect the ring. ([Check ring guide](https://www.imspares.com/injection-molding-machine-parts/barrel-screw/check-ring/))
3. **Uneven mold cooling**: A blocked or restricted mold water circuit gives uneven mold temperatures and sink marks. Compare the flow of each circuit at the water manifold, and look for kinked hoses and partly closed valves. ([Cooling water manifold guide](https://www.imspares.com/injection-molding-machine-parts/hydraulics/cooling-water-manifold/))
4. **Unsteady hydraulic pressure during hold**: A worn proportional valve, a pump problem or a dirty oil filter gives inconsistent hold pressure. Compare the actual pressure with the setpoint using a calibrated gauge. ([Proportional valve guide](https://www.imspares.com/injection-molding-machine-parts/hydraulics/proportional-valve/), [Proportional valve](https://www.imspares.com/parts/hy-cv-04/), [Oil filter guide](https://www.imspares.com/injection-molding-machine-parts/hydraulics/oil-filter/))

### Black specks, streaks or burn marks

Black specks come from plastic that has degraded in the melt path: a zone running too hot, melt hanging up in a worn spot, or material staying too long in the barrel. Burn marks at the last area to fill can instead point to trapped air at the vents.

URL: https://www.imspares.com/troubleshooting/#black-specks

1. **A zone running too hot, or a thermocouple reading low**: Compare the displayed temperature with a calibrated handheld probe at the thermocouple position. A thermocouple that has slipped out of its hole reads low, so the zone overheats without an alarm. ([Thermocouple guide](https://www.imspares.com/injection-molding-machine-parts/heaters/thermocouple/), [Thermocouple sensor](https://www.imspares.com/parts/ec-ht-02/))
2. **Settings that overheat the melt or keep it too long in the barrel**: Very high back pressure or screw speed adds shear heat that degrades heat-sensitive materials. A shot that uses only a small share of the barrel's capacity also leaves the plastic in the barrel for many cycles. ([Back pressure guide](https://www.imspares.com/injection-molding-machine-parts/barrel-screw/back-pressure/), [Shot size guide](https://www.imspares.com/injection-molding-machine-parts/barrel-screw/shot-size/))
3. **Melt hanging up in the screw tip, barrel head or nozzle**: Degraded plastic collects between the screw tip, seat ring and screw face, in a gap at the barrel head joint, and in dead spots of a shut-off nozzle or nozzle filter. Inspect these parts each time the screw tip is changed or the screw is pulled. ([Screw tip guide](https://www.imspares.com/injection-molding-machine-parts/barrel-screw/screw-tip/), [Barrel head guide](https://www.imspares.com/injection-molding-machine-parts/barrel-screw/barrel-head/), [Shut-off nozzle guide](https://www.imspares.com/injection-molding-machine-parts/barrel-screw/shut-off-nozzle/))
4. **Worn screw and barrel**: More black specks together with slower color changes, a varying cushion and longer recovery point to wear. Pull the screw and measure the flights and the bore. ([Barrel and screw guide](https://www.imspares.com/injection-molding-machine-parts/barrel-screw/), [Measuring wear article](https://www.imspares.com/blog/measuring-barrel-screw-wear-injection-molding/), [Bimetallic barrel and screw](https://www.imspares.com/parts/mc-bc-01/))
5. **Trapped air at the mold vents**: Burns or discoloration at the last area to fill come from air compressed in blocked or shallow vents. Too much clamping force can also close the vents over time. ([Short shots article](https://www.imspares.com/blog/short-shots-injection-molding-causes-fixes/), [Clamping force guide](https://www.imspares.com/injection-molding-machine-parts/toggle/clamping-force/))

### Shot weight or cushion varies from shot to shot

An unstable cushion is most often a worn check ring. Rule it out before changing the process or opening the injection cylinder.

URL: https://www.imspares.com/troubleshooting/#shot-weight-varies

1. **Worn check ring**: A cushion that varies or runs to zero, a screw that drifts forward during hold, and longer injection time at the same speed setting point to the ring. Replace the tip, ring and seat as a set. ([Check ring guide](https://www.imspares.com/injection-molding-machine-parts/barrel-screw/check-ring/), [Screw head wrench](https://www.imspares.com/parts/mc-gmp-01/))
2. **Uneven feeding**: A partial bridge, a low hopper level, a half-closed slide gate or a magnet grate blocked with fines starves the screw. Recovery time that varies from shot to shot is the usual sign. ([Hopper and feed throat guide](https://www.imspares.com/injection-molding-machine-parts/barrel-screw/hopper-and-feed-throat/))
3. **Worn screw and barrel**: If shot weight and cushion still vary after the check ring has been replaced, measure the screw flights and the barrel bore. ([Screw guide](https://www.imspares.com/injection-molding-machine-parts/barrel-screw/screw/), [Injection screw](https://www.imspares.com/parts/mc-bc-02/), [Measuring wear article](https://www.imspares.com/blog/measuring-barrel-screw-wear-injection-molding/))
4. **Hot oil or an unsteady proportional valve**: If the cushion becomes less stable as the shift goes on, check the oil temperature. If the fill time varies while the settings stay the same, check the proportional valve against a calibrated gauge. ([Oil temperature guide](https://www.imspares.com/injection-molding-machine-parts/hydraulics/oil-temperature/), [Proportional valve guide](https://www.imspares.com/injection-molding-machine-parts/hydraulics/proportional-valve/))
5. **Worn linear transducer**: If the cushion or shot size reading varies although the process has not changed, move the screw slowly in manual mode and watch for a jump in the position at the same point. ([Linear transducer guide](https://www.imspares.com/injection-molding-machine-parts/electrical/linear-transducer/))

## Screw, barrel and nozzle

Problems with screw recovery, the nozzle and the screw drive of the injection unit.

### Screw recovery is slow or fails

First check whether the screw turns at its set speed. If it does, look at feeding, barrel temperatures and screw wear; if it turns slower than set, look at the hydraulic supply, the control valve and the plasticizing motor.

URL: https://www.imspares.com/troubleshooting/#slow-recovery

1. **Material not feeding**: If the screw turns but does not move back, no material is reaching it: look for an empty hopper, a closed slide gate or a bridge. A feed throat that runs hot because its cooling water is off, low or scaled makes the pellets bridge. ([Hopper and feed throat guide](https://www.imspares.com/injection-molding-machine-parts/barrel-screw/hopper-and-feed-throat/), [Cooling water manifold guide](https://www.imspares.com/injection-molding-machine-parts/hydraulics/cooling-water-manifold/))
2. **A rear or middle zone running cold**: Unmelted pellets, high screw torque and slow recovery point to a cold zone. Look for a zone below its set point with its output high, and check its bands. ([Barrel temperature zones guide](https://www.imspares.com/injection-molding-machine-parts/heaters/barrel-temperature-zones/), [Ceramic heater band](https://www.imspares.com/parts/ec-ht-01/))
3. **Back pressure set high**: Very high back pressure lengthens recovery, which can become longer than the cooling time. Use the lowest setting that gives consistent parts. ([Back pressure guide](https://www.imspares.com/injection-molding-machine-parts/barrel-screw/back-pressure/))
4. **Worn screw and barrel**: Recovery that takes longer at the same screw speed and back pressure points to worn flights or a worn bore. Measure both when the screw is pulled, which is done with the barrel hot. ([Screw guide](https://www.imspares.com/injection-molding-machine-parts/barrel-screw/screw/), [Injection screw](https://www.imspares.com/parts/mc-bc-02/), [Bimetallic barrel and screw](https://www.imspares.com/parts/mc-bc-01/))
5. **Plasticizing motor or its supply**: If the screw turns slower than set, or its speed drops as the load rises, check the valve, its signal and the hydraulic supply before the motor. A worn motor leaks internally, so it turns slower for the same flow and runs hotter. ([Plasticizing motor guide](https://www.imspares.com/injection-molding-machine-parts/injection-unit/plasticizing-motor/), [Hydraulic plasticizing motor](https://www.imspares.com/parts/hy-pw-08/))

### Material drools or leaks at the nozzle

Drool between shots is often a setting: nozzle temperature, back pressure or decompression. Melt leaking around the tip or at a joint usually points to a fit or seal problem.

URL: https://www.imspares.com/troubleshooting/#nozzle-drool

1. **Nozzle too hot, too little decompression or too much back pressure**: Set decompression (suck-back) after recovery, reduce the back pressure, and lower the nozzle temperature in small steps. Too much decompression draws air into the nozzle. ([Nozzle problems article](https://www.imspares.com/blog/injection-nozzle-problems-troubleshooting/), [Back pressure guide](https://www.imspares.com/injection-molding-machine-parts/barrel-screw/back-pressure/))
2. **Nozzle and sprue bushing do not match, are off center or do not seal**: The nozzle tip radius should be the same as or slightly smaller than the sprue bushing radius, and the orifice slightly smaller than the bushing opening. Coat the tip thinly with marking paste and bring it against the mold: the print should be an even ring around the orifice. Too little nozzle contact force also lets melt leak at the joint. ([Nozzle guide](https://www.imspares.com/injection-molding-machine-parts/barrel-screw/nozzle/), [Locating ring guide](https://www.imspares.com/injection-molding-machine-parts/platens/locating-ring/))
3. **Worn nozzle tip or shut-off valve**: Look for an orifice worn larger than its original size, dents or a flattened ring on the tip radius, and a damaged seat. On a shut-off nozzle, a worn needle or seat, degraded plastic on the seat or a weak spring stops it closing. ([Shut-off nozzle guide](https://www.imspares.com/injection-molding-machine-parts/barrel-screw/shut-off-nozzle/), [Injection nozzle](https://www.imspares.com/parts/mc-bc-07/))
4. **Leak at the barrel head or the nozzle thread**: Plastic oozing from the joint between the head and the barrel, or at the nozzle thread, means dirty or damaged faces, or bolts not tightened in sequence to torque. Starting on plastic that is not fully melted can also push melt into the joint. ([Barrel head guide](https://www.imspares.com/injection-molding-machine-parts/barrel-screw/barrel-head/), [Barrel front flange](https://www.imspares.com/parts/mc-bc-08/))
5. **Nozzle off center from worn carriage guides**: Worn linear guides or guide bushings let the nozzle sit off center, so melt leaks at the joint. With the machine locked off and the carriage cylinders depressurized, check the carriage for play with a dial indicator. ([Linear guide rail guide](https://www.imspares.com/injection-molding-machine-parts/injection-unit/linear-guide/), [Linear guide rail and slider](https://www.imspares.com/parts/mc-sg-08/))

### Nozzle blocked or freezing

A blocked nozzle shows as a high injection pressure alarm or short shots. A nozzle that freezes is losing more heat than its heater supplies.

URL: https://www.imspares.com/troubleshooting/#nozzle-blocked

1. **Nozzle heater not heating or loose**: Check that the heater works and is tight on the nozzle body. With the injection unit retracted, the heater power locked off and the nozzle cooled to a safe handling temperature, measure its resistance and insulation. ([Nozzle heater guide](https://www.imspares.com/injection-molding-machine-parts/heaters/nozzle-heater/), [Ceramic heater band](https://www.imspares.com/parts/ec-ht-01/))
2. **Nozzle thermocouple in the wrong place**: The thermocouple must sit fully in its seat in the nozzle body, not on or against the heater band. On the band it measures the heater, and the nozzle can run much colder than the display shows. ([Thermocouple guide](https://www.imspares.com/injection-molding-machine-parts/heaters/thermocouple/), [Thermocouple sensor](https://www.imspares.com/parts/ec-ht-02/))
3. **Long contact with the cold mold**: Check how long the nozzle stays against the cold sprue bushing between shots. Long dwell times and pauses let the tip freeze and send cold slugs into the part. ([Nozzle problems article](https://www.imspares.com/blog/injection-nozzle-problems-troubleshooting/))
4. **Cold start or degraded material**: Injecting before the barrel and nozzle have soaked pushes a cold slug into the orifice, and material left too long at temperature carbonizes. Remove the nozzle while hot, clean it with brass tools, and replace it if the bore is pitted or heavily carboned. ([Nozzle guide](https://www.imspares.com/injection-molding-machine-parts/barrel-screw/nozzle/), [Injection nozzle](https://www.imspares.com/parts/mc-bc-07/))
5. **Blocked nozzle filter or a metal fragment**: A blocked nozzle filter looks like a blocked nozzle. A piece of a broken screw tip or check ring can also lodge in the nozzle: stop the machine and inspect the tip set. ([Nozzle filter guide](https://www.imspares.com/injection-molding-machine-parts/barrel-screw/nozzle-filter/), [Screw tip guide](https://www.imspares.com/injection-molding-machine-parts/barrel-screw/screw-tip/))

### Noise, knocking or vibration from the screw drive

Note when the noise happens. A clunk as rotation starts points to the drive connection, uneven rotation to the motor, and a judder or knock as the screw drive travels to its guides or the piston rod.

URL: https://www.imspares.com/troubleshooting/#screw-drive-noise

1. **Worn drive spline, key or sleeve**: Play or a clunk when rotation starts comes from a worn shaft spline, key or drive sleeve. Look for play at the drive connection with the machine stopped and locked out. ([Plasticizing motor guide](https://www.imspares.com/injection-molding-machine-parts/injection-unit/plasticizing-motor/), [Hydraulic plasticizing motor](https://www.imspares.com/parts/hy-pw-08/))
2. **Worn plasticizing motor**: Uneven or pulsing rotation, knocking, or a motor that runs hotter than usual points to internal wear. Check the valve, its signal and the hydraulic supply first. ([Plasticizing motor guide](https://www.imspares.com/injection-molding-machine-parts/injection-unit/plasticizing-motor/), [Hydraulic plasticizing motor](https://www.imspares.com/parts/hy-pw-08/))
3. **Worn guide column bushings or loose column nuts**: Jerky movement, squeaking or juddering of the moving plate, and knocking at the start or end of the stroke point to the guide columns. Release the pressure and lock off the machine, then measure the play at each bushing with a dial indicator and check the column nuts. ([Guide columns guide](https://www.imspares.com/injection-molding-machine-parts/injection-unit/guide-columns/), [Bushings and guides](https://www.imspares.com/categories/mechanical/bushings-guides/))
4. **Loose injection piston rod end**: Knocking at the start of injection or when the movement reverses can come from a loose rod end. Check the lock nut and the rod end for movement and fretting marks. ([Injection piston rod guide](https://www.imspares.com/injection-molding-machine-parts/injection-unit/injection-piston-rod/), [Injection piston rod](https://www.imspares.com/parts/mc-gz-01/))

## Barrel and nozzle heating

Barrel and nozzle zones that do not heat, run above their set point, or keep losing heater bands.

### A heater zone does not heat or never reaches its set point

Read the actual temperature and the output percentage together: a zone below its set point while its output is high or at 100% has a band, wiring, fuse or relay fault. Heater bands run on mains voltage, so lock off the heater supply and check the terminals are dead before touching them.

URL: https://www.imspares.com/troubleshooting/#zone-not-heating

1. **Heater band burnt open**: With the heaters on, a clamp meter on each band's cable shows which band draws no current. Then lock off the supply and measure that band's resistance: an open circuit means a broken element. ([Heater band types guide](https://www.imspares.com/injection-molding-machine-parts/heaters/heater-band-types/), [Ceramic heater band](https://www.imspares.com/parts/ec-ht-01/))
2. **Loose heater band**: A band that is not tight on the barrel heats the zone poorly, runs hot and fails early. Check the clamp bolts, and re-tighten a new band once the zone has reached temperature, following your site's procedure for working near hot parts. ([Replacing heater bands guide](https://www.imspares.com/injection-molding-machine-parts/heaters/replacing-heater-bands/))
3. **Broken cable, tripped fuse, a relay that does not switch or a band on the wrong voltage**: If the bands test good, check the cable and terminals, the fuse or breaker, and the relay; a band rated for a higher voltage than the supply never reaches its output. If the earth leakage breaker trips when the heaters switch on, test the insulation between each band's terminals and its shell. ([Temperature control guide](https://www.imspares.com/injection-molding-machine-parts/heaters/temperature-control/), [Heaters guide](https://www.imspares.com/injection-molding-machine-parts/heaters/))
4. **Thermocouple open circuit**: Most controllers raise a sensor break alarm and stop heating the zone when the thermocouple breaks; check what yours does in the manual. Disconnect it and check it for continuity with a multimeter. ([Thermocouple guide](https://www.imspares.com/injection-molding-machine-parts/heaters/thermocouple/), [Thermocouple sensor](https://www.imspares.com/parts/ec-ht-02/))

### A zone overshoots its set point, swings, or the reading jumps

If the zone is above its set point with its output at 0%, the heat comes from the screw or the heater is on when it should be off. A reading that jumps usually points to the thermocouple or its cable.

URL: https://www.imspares.com/troubleshooting/#zone-overshoots

1. **Shear heat from the screw**: Shear heat from the screw and from back pressure can push a front zone above its set point with the heater off. If the output is at 0% and the hardware checks out, the cause is in the process or the screw, not the heaters. ([Back pressure guide](https://www.imspares.com/injection-molding-machine-parts/barrel-screw/back-pressure/), [Barrel temperature zones guide](https://www.imspares.com/injection-molding-machine-parts/heaters/barrel-temperature-zones/))
2. **Relay stuck closed**: Put a clamp meter on the heater cable: current flowing while the output is off points to a relay stuck closed. ([Temperature control guide](https://www.imspares.com/injection-molding-machine-parts/heaters/temperature-control/))
3. **Thermocouple out of its hole**: A probe that is not pushed home reads too low, so the controller keeps heating and the zone overheats without an alarm. Check that it is fully seated, and compare the reading with a calibrated handheld probe. ([Thermocouple guide](https://www.imspares.com/injection-molding-machine-parts/heaters/thermocouple/), [Thermocouple sensor](https://www.imspares.com/parts/ec-ht-02/))
4. **Thermocouples swapped between zones**: One zone overshooting while its neighbor never reaches temperature is the typical sign, often after maintenance. Labeling each band cable and thermocouple with its zone prevents it. ([Thermocouple guide](https://www.imspares.com/injection-molding-machine-parts/heaters/thermocouple/))
5. **Damaged thermocouple cable, poor contact or control settings**: A reading that jumps when the cable is moved means a damaged cable or connector. A zone that swings around its set point after a band or thermocouple change may need auto-tuning, following the machine manual. ([Temperature control guide](https://www.imspares.com/injection-molding-machine-parts/heaters/temperature-control/), [Thermocouple sensor](https://www.imspares.com/parts/ec-ht-02/))

### Heater bands fail often

Repeated band failures usually have a cause that the new band inherits. Find it before fitting another band of the same type, size, power and voltage.

URL: https://www.imspares.com/troubleshooting/#heater-bands-failing

1. **Loose clamp**: An air gap under the band makes the element run hot. Re-tighten new bands after the first heat-up, and check the clamps at planned stops. ([Replacing heater bands guide](https://www.imspares.com/injection-molding-machine-parts/heaters/replacing-heater-bands/), [Ceramic heater band](https://www.imspares.com/parts/ec-ht-01/))
2. **Plastic leaking under the band**: Melt from a leaking barrel head or nozzle seat gets under the band and burns it; on the nozzle heater this is the most common cause. Fix the leak and keep purged material away from the bands. ([Nozzle heater guide](https://www.imspares.com/injection-molding-machine-parts/heaters/nozzle-heater/), [Barrel head guide](https://www.imspares.com/injection-molding-machine-parts/barrel-screw/barrel-head/))
3. **Wrong voltage**: A band rated for a lower voltage than the supply burns out quickly. Compare the voltage on the band's label with the supply shown on the electrical drawing. ([Heater band types guide](https://www.imspares.com/injection-molding-machine-parts/heaters/heater-band-types/))
4. **Damaged wiring or moisture**: Burnt terminals and brittle cable cause open circuits and shorts. Bands kept in a damp place, or on a machine stored for a long time, can show low insulation; follow the band maker's advice before powering them. ([Replacing heater bands guide](https://www.imspares.com/injection-molding-machine-parts/heaters/replacing-heater-bands/))
5. **Thermocouple out of place**: A thermocouple out of its hole, or held against the outside of a nozzle band, keeps the heater on, and the band can burn out. Check that each thermocouple sits fully in its hole in the barrel or the nozzle body. ([Thermocouple guide](https://www.imspares.com/injection-molding-machine-parts/heaters/thermocouple/), [Nozzle heater guide](https://www.imspares.com/injection-molding-machine-parts/heaters/nozzle-heater/))

## Hydraulic system

Speed, pressure, temperature, noise and leak problems in the hydraulic system and its cylinders.

### Movements are slow or weak

Work from the supply outward: oil level, temperature and filter first, then the pressure at the pump outlet, then the valves and cylinder of the slow movement. If only one movement is affected, the fault is usually in that movement's circuit.

URL: https://www.imspares.com/troubleshooting/#slow-movements

1. **Low oil level, clogged filter or cold oil**: Check the level in the sight glass and the filter's clogging indicator. Cold, thick oil makes movements sluggish until it reaches its working temperature. ([Oil filter guide](https://www.imspares.com/injection-molding-machine-parts/hydraulics/oil-filter/), [Hydraulic oil filter](https://www.imspares.com/parts/o-tc-02/), [Oil temperature guide](https://www.imspares.com/injection-molding-machine-parts/hydraulics/oil-temperature/))
2. **Relief or proportional valve not holding pressure**: Fit a calibrated gauge at the pump outlet and compare it with the setpoint in manual mode. A low reading there points to the pump or the relief valve; a correct reading points further down the circuit. ([Hydraulic pressure loss article](https://www.imspares.com/blog/troubleshooting-hydraulic-pressure-loss/), [Relief valve guide](https://www.imspares.com/injection-molding-machine-parts/hydraulics/relief-valve/))
3. **Worn pump**: Movements slower at the same settings, pressure that falls under load, and a louder, hotter pump point to wear. Rule out the suction side, the relief valve and the coupling first, since they cause the same symptoms. ([Hydraulic pump guide](https://www.imspares.com/injection-molding-machine-parts/hydraulics/hydraulic-pump/), [Vane pump](https://www.imspares.com/parts/hy-pw-06/), [Piston pump](https://www.imspares.com/parts/hy-pw-07/))
4. **Directional valve spool sticking or worn**: A spool that shifts only part way, or oil leaking across worn spool lands, makes one movement slow or weak. Check the controller output and the voltage at the connector, then whether the spool moves with the manual override. ([Directional valve guide](https://www.imspares.com/injection-molding-machine-parts/hydraulics/directional-valve/), [Directional control valve](https://www.imspares.com/parts/hy-cv-02/))
5. **Piston seals passing oil**: The cylinder is slower and weaker under load and may creep when its valve is closed. A bypass test at the end of the stroke shows whether oil passes the piston; a leaking valve gives the same symptoms. ([Piston seals guide](https://www.imspares.com/injection-molding-machine-parts/clamp-cylinder/piston-seals/), [Cylinder seals and Y-rings](https://www.imspares.com/parts/mc-sb-08/))
6. **Low accumulator pre-charge**: On machines with an accumulator, injection that is slower than set or falls off during the fill, with the accumulator emptying quickly at the start, points to low pre-charge. Check it with the oil side drained to zero pressure, and top up with dry nitrogen only. ([Accumulator guide](https://www.imspares.com/injection-molding-machine-parts/hydraulics/accumulator/), [Hydraulic accumulator](https://www.imspares.com/parts/hy-au-02/))

### Pressure drops or cannot reach the set value

Measure the pressure at the pump outlet with a calibrated gauge and compare it with the setpoint. A low reading there points to the supply; a correct reading with weak movements points to leakage further down the circuit.

URL: https://www.imspares.com/troubleshooting/#pressure-loss

1. **Low oil level or blocked suction filter**: The pump cannot draw enough oil and cavitates. Read the sight glass with the machine in the condition the manual specifies, and check the filter indicator. ([Oil tank guide](https://www.imspares.com/injection-molding-machine-parts/hydraulics/oil-tank/), [Oil filter guide](https://www.imspares.com/injection-molding-machine-parts/hydraulics/oil-filter/), [Hydraulic oil filter](https://www.imspares.com/parts/o-tc-02/))
2. **Relief valve opening too early**: Dirt, a worn seat or a weak spring opens it too early, and in a pilot-operated valve a blocked damping orifice lets the main stage open at low pressure. Only a trained technician should adjust it, with a calibrated gauge and the values in the machine manual. ([Relief valve guide](https://www.imspares.com/injection-molding-machine-parts/hydraulics/relief-valve/), [Relief valve](https://www.imspares.com/parts/hy-cv-06/))
3. **Worn pump**: On a piston pump, measure the case drain flow under load and compare it with the pump maker's limit. On a servo machine, a motor that runs faster than before during hold points to internal leakage in the pump, valves or cylinders. ([Hydraulic pump guide](https://www.imspares.com/injection-molding-machine-parts/hydraulics/hydraulic-pump/), [Vane pump](https://www.imspares.com/parts/hy-pw-06/), [Piston pump](https://www.imspares.com/parts/hy-pw-07/), [Gear pump](https://www.imspares.com/parts/hy-pw-02/))
4. **Proportional valve or pressure transducer**: Compare the actual pressure with the setpoint at several values; pressure that stays the same whatever the setting points to the proportional valve. On a servo pump machine, a transducer that reads wrong gives the same symptom. ([Proportional valve guide](https://www.imspares.com/injection-molding-machine-parts/hydraulics/proportional-valve/), [Pressure transducer guide](https://www.imspares.com/injection-molding-machine-parts/hydraulics/pressure-transducer/), [Proportional valve](https://www.imspares.com/parts/hy-cv-04/))
5. **Internal leakage in a valve or cylinder**: If the pump outlet pressure is correct, use the circuit diagram and action table to list the valves and cylinder of the weak movement, then test them. Lock out and relieve the pressure, including the accumulator, before opening anything. ([Hydraulic circuit guide](https://www.imspares.com/injection-molding-machine-parts/hydraulics/hydraulic-circuit/), [Hydraulic check valve guide](https://www.imspares.com/injection-molding-machine-parts/hydraulics/hydraulic-check-valve/), [Cartridge valve guide](https://www.imspares.com/injection-molding-machine-parts/hydraulics/cartridge-valve/))

### Hydraulic oil is overheating

Heat comes from oil losing pressure without doing work. Check the cooling water first; if the cooler is working, find the component that is making the heat.

URL: https://www.imspares.com/troubleshooting/#oil-overheating

1. **Cooling water off, low or too warm**: Check that the water valve is open, the strainer is clean and the supply is cool. Measure the water temperature into and out of the cooler: water leaving very warm means the flow is too low. ([Oil temperature guide](https://www.imspares.com/injection-molding-machine-parts/hydraulics/oil-temperature/), [Cooling water manifold guide](https://www.imspares.com/injection-molding-machine-parts/hydraulics/cooling-water-manifold/))
2. **Fouled oil cooler**: If the oil is hot but the water leaves the cooler barely warmer than it entered, scale, mud or algae on the water side are stopping the heat. A small oil temperature difference across the cooler while the water flows well points the same way. ([Oil cooler guide](https://www.imspares.com/injection-molding-machine-parts/hydraulics/oil-cooler/), [Oil cooler](https://www.imspares.com/parts/o-tc-04/))
3. **Relief valve dumping oil**: With the cooler working, look for components much hotter than the rest with an infrared thermometer; a hot relief valve and return line show oil passing. Also check the system relief setting and, on fixed pump machines, the unloading during idle times. ([Relief valve guide](https://www.imspares.com/injection-molding-machine-parts/hydraulics/relief-valve/), [Relief valve](https://www.imspares.com/parts/hy-cv-06/))
4. **Worn pump leaking internally**: A pump case running hotter than usual, with slower movements, points to internal leakage. On a piston pump, more oil comes out of the case drain. ([Hydraulic pump guide](https://www.imspares.com/injection-molding-machine-parts/hydraulics/hydraulic-pump/), [Vane pump](https://www.imspares.com/parts/hy-pw-06/), [Piston pump](https://www.imspares.com/parts/hy-pw-07/))
5. **Leaking cylinder seals, low oil level or wrong oil**: Oil forced through a leaking piston seal turns pressure into heat, and a low level puts the same heat into less oil. Check the level, and that the oil grade matches the machine manual. ([Piston seals guide](https://www.imspares.com/injection-molding-machine-parts/clamp-cylinder/piston-seals/), [Hydraulic oil guide](https://www.imspares.com/injection-molding-machine-parts/hydraulics/hydraulic-oil/))

### Hydraulic pump is noisy

Most pump noise starts on the suction side, from cavitation or air. Check the oil and the suction side before replacing the pump.

URL: https://www.imspares.com/troubleshooting/#noisy-pump

1. **Cavitation at the suction**: A whine or rattle, worst when the oil is cold, points to a blocked suction filter, a low oil level or a suction valve that is not fully open. Check all three. ([Oil filter guide](https://www.imspares.com/injection-molding-machine-parts/hydraulics/oil-filter/), [Hydraulic oil filter](https://www.imspares.com/parts/o-tc-02/))
2. **Air drawn into the oil**: Foam in the tank means air is getting in, through a suction line leak, a worn pump shaft seal, a low level or a return line that ends above the oil surface. Check the suction connections with soapy water. ([Oil tank guide](https://www.imspares.com/injection-molding-machine-parts/hydraulics/oil-tank/), [Hydraulic oil problems article](https://www.imspares.com/blog/hydraulic-oil-problems-injection-molding/))
3. **Worn coupling insert or misalignment**: A knock at start-up or when the pressure changes, rubber dust in or under the bell housing and more vibration point to the coupling. Lock out the motor, and on a servo motor wait for the drive to discharge, before inspecting the insert. ([Pump coupling guide](https://www.imspares.com/injection-molding-machine-parts/hydraulics/pump-coupling/), [Pump coupling and bell housing](https://www.imspares.com/parts/hy-pw-05/))
4. **Worn pump**: Noise that grows over time, with slower movements and hotter oil, points to wear inside the pump. Metal particles in the suction filter or on the drain plug magnet confirm it. ([Vane pump guide](https://www.imspares.com/injection-molding-machine-parts/hydraulics/vane-pump/), [Vane pump](https://www.imspares.com/parts/hy-pw-06/), [Piston pump](https://www.imspares.com/parts/hy-pw-07/))
5. **Relief valve squealing**: A squeal, whistle or chatter from the relief valve means oil is flowing through it at high pressure. The setting may be too close to the working pressure, or the valve is worn. ([Relief valve guide](https://www.imspares.com/injection-molding-machine-parts/hydraulics/relief-valve/))

### Oil leaking at a cylinder

Oil on a piston rod or dripping from the front head is usually the rod seal or wiper. Inspect the rod surface as well, because a damaged rod cuts new seals on every stroke.

URL: https://www.imspares.com/troubleshooting/#cylinder-oil-leak

1. **Worn rod seal or wiper**: Oil drips from the front head, or an oil ring builds up on the rod at the end of each stroke. Replace the rod seal, wiper, guide rings and O-rings together as one set. ([Rod seals guide](https://www.imspares.com/injection-molding-machine-parts/clamp-cylinder/rod-seals/), [Piston rod seal set](https://www.imspares.com/parts/mc-sb-07/))
2. **Damaged piston rod**: Run a fingernail across any mark on the rod: a mark you can feel will cut new seals. Pitting or flaking chrome also means the rod needs re-chroming and grinding, or replacing. ([Injection piston rod guide](https://www.imspares.com/injection-molding-machine-parts/injection-unit/injection-piston-rod/), [Injection piston rod](https://www.imspares.com/parts/mc-gz-01/))
3. **Side load on the rod**: Uneven wear on one side of the old seals and guide ring shows the rod runs off center. On a toggle machine, worn crosshead guides can push the clamping cylinder rod sideways. ([Crosshead guide](https://www.imspares.com/injection-molding-machine-parts/toggle/crosshead/), [Crosshead](https://www.imspares.com/parts/mc-cr-02/))
4. **Hot or dirty oil**: Oil running too hot hardens seals, and dirt carried in past a worn wiper wears the seal and the rod. Check the oil temperature and condition. ([Oil temperature guide](https://www.imspares.com/injection-molding-machine-parts/hydraulics/oil-temperature/), [Hydraulic oil guide](https://www.imspares.com/injection-molding-machine-parts/hydraulics/hydraulic-oil/))
5. **Loose fittings or hoses**: At the ejector cylinder, loose fittings and hoses are the other usual source of oil on the platen or the mold. Switch off, lock out and release the hydraulic pressure before opening any fitting. ([Ejector cylinder guide](https://www.imspares.com/injection-molding-machine-parts/ejector/ejector-cylinder/))

### Movements are jerky or uneven

Jerky movements usually come from air in the oil or from a valve that does not respond smoothly. Check the oil level and look for foam first.

URL: https://www.imspares.com/troubleshooting/#jerky-movements

1. **Air in the oil**: A low level or a suction leak lets the pump draw air, so movements become jerky and spongy. Top up and check the suction side, and after seal work bleed the cylinder by moving it slowly at low pressure. ([Oil tank guide](https://www.imspares.com/injection-molding-machine-parts/hydraulics/oil-tank/), [Hydraulic oil problems article](https://www.imspares.com/blog/hydraulic-oil-problems-injection-molding/))
2. **Sticking valve spool**: Dirt and varnish make a spool stick in its bore, and over-tightened mounting bolts can distort the valve body. Check the oil cleanliness and whether the spool moves with the manual override. ([Directional valve guide](https://www.imspares.com/injection-molding-machine-parts/hydraulics/directional-valve/), [Directional control valve](https://www.imspares.com/parts/hy-cv-02/))
3. **Faulty proportional valve or amplifier**: Pressure that jumps or oscillates, or a slow start to a movement, points to the proportional valve. Check that the coil current changes with the command, and bleed the valve if it has a bleed screw. ([Proportional valve guide](https://www.imspares.com/injection-molding-machine-parts/hydraulics/proportional-valve/), [Proportional valve](https://www.imspares.com/parts/hy-cv-04/))
4. **Faulty pressure transducer on a servo machine**: On a servo pump machine, pressure that hunts or oscillates, or a reading that changes when you move the cable, points to the transducer or its cable. Compare it with a calibrated gauge fitted at the same point. ([Pressure transducer guide](https://www.imspares.com/injection-molding-machine-parts/hydraulics/pressure-transducer/), [Servo pump guide](https://www.imspares.com/injection-molding-machine-parts/hydraulics/servo-pump/))

## Clamp unit

Problems closing and locking the mold, holding the clamping force, and wear in the tie bars and the toggle.

### Mold does not close or lock fully

If the mold will not start closing, check the safety gate signal first. If it closes but stops before lock-up, look at the mold height setting and the force of the clamp cylinder.

URL: https://www.imspares.com/troubleshooting/#mold-not-locking

1. **Safety gate signal missing**: The controller will not close the mold until it receives the gate-closed signal. Watch the signal on the input page while slowly closing the gate, and never bridge or bypass a gate switch. ([Safety gate guide](https://www.imspares.com/injection-molding-machine-parts/electrical/safety-gate/), [Safety switch](https://www.imspares.com/parts/ec-sf-01/))
2. **Mold height set too tight, or something blocking the movement**: If the clamp stops before lock-up or does not reach the set force, check the mold height setting for this mold and look for anything blocking the movement. ([Mold height adjustment guide](https://www.imspares.com/injection-molding-machine-parts/tie-bars/mold-height-adjustment/), [Toggle guide](https://www.imspares.com/injection-molding-machine-parts/toggle/))
3. **Mold height adjustment slipping or stalling**: If the adjustment motor runs but the rear platen does not move, look for a slipping gear, a sheared key or a broken chain. Adjust only with the clamp open or unloaded, never against a locked toggle. ([Mold height adjustment guide](https://www.imspares.com/injection-molding-machine-parts/tie-bars/mold-height-adjustment/), [Tie bar adjustment bushing](https://www.imspares.com/parts/mc-tc-09/))
4. **Weak clamp cylinder or hydraulic supply**: Slow closing and a slow lock-up at the same settings point to oil passing the clamp piston seals or to a pressure problem. Check the pressure before opening the cylinder. ([Clamping cylinder guide](https://www.imspares.com/injection-molding-machine-parts/clamp-cylinder/), [Clamping cylinder](https://www.imspares.com/parts/mc-cc-01/), [Hydraulic pressure loss article](https://www.imspares.com/blog/troubleshooting-hydraulic-pressure-loss/))

### Flash although the clamping force is set

If the setting is right but the mold still flashes, the actual force may be lower than set or not spread evenly. Flash on one side or one corner points to uneven clamping.

URL: https://www.imspares.com/troubleshooting/#flash-with-force-set

1. **Force changed with the mold temperature or the mold height**: On a toggle machine the force changes as the mold temperature changes, and the mold height setting can drift. Check the actual force once the mold is at working temperature. ([Mold height adjustment guide](https://www.imspares.com/injection-molding-machine-parts/tie-bars/mold-height-adjustment/), [Clamping force guide](https://www.imspares.com/injection-molding-machine-parts/toggle/clamping-force/))
2. **Worn toggle pins and bushings**: Wear in the pins and bushings lowers the force at the same setting. Where the machine has no force sensors, uneven tie bar stretch between the four bars points to wear or an adjustment problem. ([Toggle pins guide](https://www.imspares.com/injection-molding-machine-parts/toggle/toggle-pins/), [Toggle pin](https://www.imspares.com/parts/mc-tl-03/), [Toggle link bushing](https://www.imspares.com/parts/mc-tl-05/))
3. **Platens out of parallel**: With the mold removed and the faces clean, measure the distance between the platens near each corner with an inside micrometer. A machine that is not level, or a frame twisted by an uneven floor, also throws the platens out of parallel. ([Platen parallelism guide](https://www.imspares.com/injection-molding-machine-parts/platens/platen-parallelism/), [Leveling procedure guide](https://www.imspares.com/injection-molding-machine-parts/feet/leveling-procedure/))
4. **Mold not sitting flat on the platen**: Dents, burrs or weld spatter on the mold face, or dirt between the mold and the platen, let the mold rock when clamped. Clean the face and check it with a precision straight edge and feeler gauges. ([Platens guide](https://www.imspares.com/injection-molding-machine-parts/platens/), [Mold clamps guide](https://www.imspares.com/injection-molding-machine-parts/platens/mold-clamps/))

### Uneven clamping, platen drop or tie bar problems

Uneven clamping shows as flash on one side, a parallelism error or tie bars carrying different loads. Measure platen parallelism before replacing parts, and stop the machine at once if a tie bar is cracked.

URL: https://www.imspares.com/troubleshooting/#uneven-clamping

1. **Worn tie bar bushings**: The moving platen drops at the mold face or rocks when pushed, and the bars show bronze-colored smears or score marks. With the machine locked out, lift the platen gently with a jack while a dial indicator reads the rise at each bore. ([Tie bar bushings guide](https://www.imspares.com/injection-molding-machine-parts/tie-bars/tie-bar-bushings/), [Tie bar bushing](https://www.imspares.com/parts/mc-tc-07/), [Tie bar liner bushing](https://www.imspares.com/parts/mc-tc-03/))
2. **Tie bar nut loose or turned**: Look for a witness mark across the nut and the bar that no longer lines up, a gap at the nut face, or fine reddish-brown powder from fretting. Reset it following the manufacturer's procedure, because it changes how the load is shared. ([Tie bar nuts guide](https://www.imspares.com/injection-molding-machine-parts/tie-bars/tie-bar-nuts/), [Tie bar nut](https://www.imspares.com/parts/mc-tc-06/), [Tie bar end cap and lock ring](https://www.imspares.com/parts/mc-tc-13/))
3. **Mold height adjusting nuts out of step**: Flash on one corner after a mold height adjustment suggests the four nuts did not turn by the same amount. Paint marks on the nuts make this easy to see. ([Mold height adjustment guide](https://www.imspares.com/injection-molding-machine-parts/tie-bars/mold-height-adjustment/), [Tie bar adjustment bushing](https://www.imspares.com/parts/mc-tc-09/))
4. **Unequal toggle wear or a bent link**: If the upper and lower toggles do not lock at the same moment, look for uneven wear, a bent link or a crosshead that tilts as it moves. ([Toggle links guide](https://www.imspares.com/injection-molding-machine-parts/toggle/toggle-links/), [Toggle arm](https://www.imspares.com/parts/mc-tl-02/), [Crosshead guide](https://www.imspares.com/injection-molding-machine-parts/toggle/crosshead/))
5. **Damaged or cracked tie bar**: Scratches from mold changes and rust pits can start fatigue cracks. A bang during clamping or a sudden loss of force on one corner means stop the machine: a bar that breaks under load releases a great deal of energy. ([Tie bar maintenance article](https://www.imspares.com/blog/tie-bar-maintenance-replacement-guide/), [Tie bar](https://www.imspares.com/parts/mc-tc-01/))

### Knocking, squealing or wear at the toggle

Note when the noise happens: at lock-up and mold break-open, or at the start of each movement. A cracked link or a broken pin means stop the machine at once.

URL: https://www.imspares.com/troubleshooting/#toggle-noise

1. **Lubricant not reaching the joints**: Squealing, dry joints, or dark, gritty lubricant at a joint mean that point is not being supplied. Check the reservoir and the lubrication alarms, run a manual lubrication cycle, and confirm fresh lubricant appears at each joint. ([Toggle lubrication guide](https://www.imspares.com/injection-molding-machine-parts/toggle/toggle-lubrication/))
2. **Worn toggle pins and bushings**: A knock at lock-up or when the mold breaks open, play at the joints and bronze-colored particles in the lubricant point to wear. Measure the play at each joint with a dial indicator, with the clamp depressurized. ([Toggle bushings guide](https://www.imspares.com/injection-molding-machine-parts/toggle/toggle-bushings/), [Toggle pin bushing](https://www.imspares.com/parts/mc-jm-02/), [Toggle pin](https://www.imspares.com/parts/mc-tl-03/))
3. **Loose crosshead connection or worn short-link bushings**: A knock at the start of closing or opening often comes from the connection between the cylinder rod and the crosshead. Check it for fretting marks, a loose lock nut or a gap, and watch it move only at slow speed from outside the closed guards. ([Crosshead guide](https://www.imspares.com/injection-molding-machine-parts/toggle/crosshead/), [Crosshead](https://www.imspares.com/parts/mc-cr-02/), [Connecting rod bushing](https://www.imspares.com/parts/mc-jm-05/))
4. **Closing into lock-up too fast**: A speed profile that does not slow the clamp before lock-up, or a mold height set too tight, also causes a knock. Check the settings before taking the toggle apart. ([Toggle guide](https://www.imspares.com/injection-molding-machine-parts/toggle/))
5. **Loose clamp cylinder rod nut**: Knocking at each change of direction, with piston seals that keep failing or metal particles in the filter, can mean the piston rod nut has worked loose. It is reached by taking the rod and piston out of the cylinder. ([Piston rod nut guide](https://www.imspares.com/injection-molding-machine-parts/clamp-cylinder/piston-rod-nut/), [Piston rod nut](https://www.imspares.com/parts/mc-sb-10/))

## Ejector

Problems with the machine's ejector: an ejector that does not return, creeps forward, or bends its rods.

### Ejector does not return or sticks

Do not close the mold until the cause is found, and never bypass the ejector-not-back interlock: closing the mold with the ejector forward can crush the pins and damage the mold.

URL: https://www.imspares.com/troubleshooting/#ejector-not-returning

1. **Broken or tired return springs**: A spring shorter than the others, broken coils in the spring pocket, or a plate that tilts as it returns point to the springs. The springs are under load: release them in a controlled way, measure their free length against a new spring, and replace them as a set. ([Return springs guide](https://www.imspares.com/injection-molding-machine-parts/ejector/return-springs/), [Return spring](https://www.imspares.com/parts/mc-sr-05/))
2. **Connecting plate sticking or a bent rod**: Worn or scored guide pins and holes let the plate tilt and bind, and a bent rod drags in its platen hole. Check the guide pins, roll each rod on a flat surface, and remove burrs from the platen holes. ([Ejector plate guide](https://www.imspares.com/injection-molding-machine-parts/ejector/ejector-plate/), [Ejector connecting plate and pin kit](https://www.imspares.com/parts/mc-es-09/), [Ejector rod guide](https://www.imspares.com/injection-molding-machine-parts/ejector/ejector-rod/))
3. **Hydraulic valve fault or cylinder not completing its return**: Watch the ejector run at slow speed and compare the stroke time with earlier records. Check the valve that drives it before opening the cylinder. ([Ejector cylinder guide](https://www.imspares.com/injection-molding-machine-parts/ejector/ejector-cylinder/), [Directional valve guide](https://www.imspares.com/injection-molding-machine-parts/hydraulics/directional-valve/))
4. **Position sensor not detecting the return**: With nobody in the mold area, move the ejector slowly in manual mode and watch the sensor LED and the controller's input page. Check the gap to the target and clean any metal chips off the sensing face. ([Proximity sensor guide](https://www.imspares.com/injection-molding-machine-parts/electrical/proximity-sensor/), [Proximity sensor](https://www.imspares.com/parts/ec-sf-03/))
5. **Ejector creeping forward**: An ejector that will not stay back is leaking internally, past worn piston seals or through the valve that should hold it. Check the valve and test the cylinder seals. ([Ejector cylinder guide](https://www.imspares.com/injection-molding-machine-parts/ejector/ejector-cylinder/), [Piston seals guide](https://www.imspares.com/injection-molding-machine-parts/clamp-cylinder/piston-seals/))

### Ejector rods bend or break

Rods usually bend when the ejector is driven against a closed or blocked mold, or when the plate is pushed off square. Check the setup before fitting new rods.

URL: https://www.imspares.com/troubleshooting/#ejector-rods-bend

1. **Ejecting against a closed or blocked mold**: Check the ejector sequence and the interlocks for this mold. A broken rod usually fails at the thread. ([Ejector rod guide](https://www.imspares.com/injection-molding-machine-parts/ejector/ejector-rod/), [Ejector rod](https://www.imspares.com/parts/mc-es-08/))
2. **Stroke set longer than the mold allows**: Compare the stroke set on the controller with the travel the mold's ejector plate allows. Too long a stroke also squeezes the return springs beyond their rated travel. ([Ejector rod guide](https://www.imspares.com/injection-molding-machine-parts/ejector/ejector-rod/), [Return springs guide](https://www.imspares.com/injection-molding-machine-parts/ejector/return-springs/))
3. **Rods of different lengths or a tilted plate**: Measure every rod in the set: all rods used on one mold must be the same length. Worn guide pins or broken return springs can also tilt the connecting plate. ([Ejector plate guide](https://www.imspares.com/injection-molding-machine-parts/ejector/ejector-plate/), [Ejector connecting plate and pin kit](https://www.imspares.com/parts/mc-es-09/))
4. **Rods not tightened or damaged threads**: Rods that keep unscrewing, or stretched threads, let the rod work loose and take side load. Inspect the threads, and fit straight rods of the right length tightened fully. ([Ejector rod guide](https://www.imspares.com/injection-molding-machine-parts/ejector/ejector-rod/), [Ejector rod](https://www.imspares.com/parts/mc-es-08/))
5. **Ejector force set too high**: Too much ejector force bends rods, and ejection that is too fast or too forceful also marks and cracks parts. Check the force and speed settings for the mold. ([Ejector guide](https://www.imspares.com/injection-molding-machine-parts/ejector/), [Ejector pins guide](https://www.imspares.com/injection-molding-machine-parts/ejector/ejector-pins/))

## Electrical system

Faults in the safety circuit, the servo drive, the position sensors and the controller boards.

### Machine will not start a cycle or stops at the safety gate

The controller is missing a signal it needs, most often the gate-closed signal; the input/output monitor page shows which signal does not arrive. If the machine ever moves with the gate open, stop it at once and lock it out until it is repaired and tested.

URL: https://www.imspares.com/troubleshooting/#no-cycle-safety-gate

1. **Gate no longer presses the switch fully**: Worn gate rollers, runners or guides let the gate sit out of line, so the cam no longer presses the switch roller far enough. Watch the gate signal on the input page while slowly closing the gate, and check the rollers, the cam and the mountings. ([Safety gate guide](https://www.imspares.com/injection-molding-machine-parts/electrical/safety-gate/))
2. **Failed limit switch**: A qualified electrician replaces it with the machine isolated and locked out, using a switch with the same contact arrangement, actuator, mounting and rating. Test the interlock afterwards: with the gate open, the mold must not close. ([Limit switch guide](https://www.imspares.com/injection-molding-machine-parts/electrical/limit-switch/), [Safety switch](https://www.imspares.com/parts/ec-sf-01/))
3. **Damaged cable or loose connector**: An alarm that comes and goes when the gate is pushed or the machine vibrates points to a cable damaged where it flexes, or a loose terminal. Never bridge, tape or bypass a gate switch to keep running. ([Safety gate guide](https://www.imspares.com/injection-molding-machine-parts/electrical/safety-gate/), [Limit switch guide](https://www.imspares.com/injection-molding-machine-parts/electrical/limit-switch/))
4. **Proximity sensor not seeing its target**: If the cycle stops at the same step every time, a sensor may not be giving its signal. With nobody in the mold area, check its LED, the gap to the target and the cable. ([Proximity sensor guide](https://www.imspares.com/injection-molding-machine-parts/electrical/proximity-sensor/), [Proximity sensor](https://www.imspares.com/parts/ec-sf-03/))
5. **Failed input channel**: If the switch works but the controller does not see it, the I/O module input or its wiring may have failed. Compare the I/O page with the LED on the module and a meter reading at the terminal block. ([I/O module guide](https://www.imspares.com/injection-molding-machine-parts/electrical/io-module/), [I/O module](https://www.imspares.com/parts/ec-cbc-06/))

### Servo drive alarm

Read the code on the drive's own display and look it up in the drive manual before changing parts. Drive work is for qualified electricians: the DC bus capacitors hold a dangerous charge after switch-off, so wait the discharge time on the drive label and measure before touching anything.

URL: https://www.imspares.com/troubleshooting/#servo-drive-alarm

1. **Encoder cable or connector**: Encoder alarms often come from a damaged, oil-soaked or poorly shielded encoder cable, or a loose plug. Check the cable along its length and the connectors at both ends, and test with a known good cable where possible. ([Encoder guide](https://www.imspares.com/injection-molding-machine-parts/electrical/encoder/), [AC servo motor](https://www.imspares.com/parts/ec-gep-01/))
2. **Drive overheating**: A failed cooling fan, a heatsink clogged with dust or a hot cabinet trips the drive. Clean the heatsink and filters and check the fan. ([Servo drive guide](https://www.imspares.com/injection-molding-machine-parts/electrical/servo-drive/))
3. **Damaged motor cable or winding insulation**: Overcurrent or earth fault alarms point to the motor cable, the motor windings or the power module. With the machine isolated, disconnect the motor cable at the drive before testing the winding insulation, because the test voltage can damage the drive. ([Servo motor guide](https://www.imspares.com/injection-molding-machine-parts/electrical/servo-motor/), [AC servo motor](https://www.imspares.com/parts/ec-gep-01/))
4. **Overload from a hydraulic leak**: An overload alarm can mean the motor has worked above its rating for too long, often because of an internal leak. A motor that runs faster than usual during hold points to leakage in the pump, valves or cylinders. ([Servo pump guide](https://www.imspares.com/injection-molding-machine-parts/hydraulics/servo-pump/), [Gear pump](https://www.imspares.com/parts/hy-pw-02/))
5. **Aged DC bus capacitors or a braking fault**: DC bus voltage alarms, or a drive that trips during fast movements but runs at light load, point to aged capacitors; overvoltage can also come from a failed braking resistor. Look for bulging vents or leaking electrolyte on the capacitors. ([Capacitors guide](https://www.imspares.com/injection-molding-machine-parts/electrical/capacitors/), [Electrolytic capacitor](https://www.imspares.com/parts/ec-ce-01/))

### Position reading jumps or is unstable

Move the axis slowly in manual mode and watch the position on the panel. A jump at the same point every time points to the transducer track; a jump when the cable moves points to the wiring.

URL: https://www.imspares.com/troubleshooting/#position-unstable

1. **Worn transducer track**: On a potentiometric transducer, the track wears at positions passed every cycle, such as the mold-closed or cushion position. After fitting a new one, calibrate the zero and full-stroke positions in the controller. ([Linear transducer guide](https://www.imspares.com/injection-molding-machine-parts/electrical/linear-transducer/))
2. **Loose mounting or misaligned rod**: Loose brackets, a misaligned mounting or a seized ball joint let the body or the rod move and wear. Check them for play or binding. ([Linear transducer guide](https://www.imspares.com/injection-molding-machine-parts/electrical/linear-transducer/))
3. **Damaged cable, oily connector or electrical noise**: Check the cable and the connector for damage and oil. A poorly shielded cable picks up electrical noise, so check that the shield is connected. ([Linear transducer guide](https://www.imspares.com/injection-molding-machine-parts/electrical/linear-transducer/))
4. **Unstable reference voltage**: An unstable supply from the power supply board makes the reading unsteady. Have an electrician measure its outputs under load; an oscilloscope shows short dips that a meter misses. ([Power supply board guide](https://www.imspares.com/injection-molding-machine-parts/electrical/power-supply-board/), [Power supply board](https://www.imspares.com/parts/ec-cbc-14/))
5. **Loose piston rod nut in the cylinder**: If the rod starts to move a moment after the valve switches and the position jumps, the piston may be moving on its rod. The nut is reached by taking the rod and piston out of the cylinder. ([Piston rod nut guide](https://www.imspares.com/injection-molding-machine-parts/clamp-cylinder/piston-rod-nut/), [Piston rod nut](https://www.imspares.com/parts/mc-sb-10/))

### A board or module fails, or the controller restarts

Many apparent board faults come from the power supply, a loose connector or a fault in the field wiring, so check those first and fix the field cause before fitting a new board. Board work is for qualified electricians with the machine isolated and locked out, wearing an earthed wrist strap.

URL: https://www.imspares.com/troubleshooting/#board-fails

1. **Weak or noisy power supply**: Restarts or communication errors when many valves switch on, or several unrelated I/O faults at once, point to the power supply. Measure each output under its normal load before replacing a CPU or I/O board. ([Power supply board guide](https://www.imspares.com/injection-molding-machine-parts/electrical/power-supply-board/), [Power supply board](https://www.imspares.com/parts/ec-cbc-14/))
2. **A field fault damaging an output**: A shorted valve coil, a pinched cable touching the frame or a missing suppressor on a coil damages outputs, and a new board can fail in the same place. Check the coil resistance and the cable insulation first. ([I/O module guide](https://www.imspares.com/injection-molding-machine-parts/electrical/io-module/), [I/O module](https://www.imspares.com/parts/ec-cbc-06/))
3. **Loose connector or flat backup battery**: Communication alarms, restarts and settings lost after power-off often come from a loose connector or a flat backup battery rather than the CPU board. Back up the mold data and machine parameters before any board change. ([Controller guide](https://www.imspares.com/injection-molding-machine-parts/electrical/controller/), [Main CPU board](https://www.imspares.com/parts/ec-cbc-12/))
4. **Heat, dust or condensation in the cabinet**: Faults that appear only when the cabinet is hot point to blocked filters, failed fans and aged capacitors. Keep the cabinet filters clean and the fans working. ([Electrical system guide](https://www.imspares.com/injection-molding-machine-parts/electrical/), [Capacitors guide](https://www.imspares.com/injection-molding-machine-parts/electrical/capacitors/))
5. **Drive interface board**: If the panel shows a drive-not-ready or drive communication alarm while the drive itself shows no fault, check the signal cable and its shield, then the interface board. Some machines need the pressure and flow calibration repeated after it is changed. ([Drive interface board guide](https://www.imspares.com/injection-molding-machine-parts/electrical/drive-interface-board/), [Drive interface board](https://www.imspares.com/parts/ec-cbc-13/))