Hot Runner Controller Troubleshooting: Causes & Fixes

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Problems on this page:

Zone not heating Zone temperature unstable Gate drooling or stringing Gates freezing off Material leaking in the manifold Earth fault on start-up Colour or material changes taking too long Zones swapped after a mould change

Zone not heating

Hits OEE: Availability

Symptoms: One zone stays cold or shows an open circuit alarm, and the cavity it feeds runs short or not at all.

Heater burnt out

Measure the heater resistance with the mould safe and replace the heater if it is open.

Damaged wiring or connector at the mould

Inspect the cables and the connector pins for burns, bends and loose crimps.

Failed fuse or output on the controller card

Swap the zone to a spare card to find out whether the fault is in the controller or the mould.

Heater and thermocouple wired to different zones

Check the wiring against the mould drawing after every mould change.

Prevention: A zone check at each mould change with the resistances recorded.

Zone temperature unstable

Hits OEE: Quality

Symptoms: A zone swings around its setpoint or overshoots after start-up, and part quality changes with it.

Thermocouple pinched or grounded

Check the thermocouple reading against a second probe and replace a damaged one.

Wrong thermocouple type selected

Match the controller setting to the thermocouple type in the mould.

Control loop not tuned for the zone

Run the auto-tune with the mould at operating conditions.

Heater too large or too small for the zone

Check the heater wattage against the zone.

Prevention: Zone temperature and output percentage trended during production.

Gate drooling or stringing

Hits OEE: Quality

Symptoms: Material drips from the gate between shots or strings appear on the parts.

Nozzle tip temperature too high

Lower the tip temperature in small steps.

Decompression too low

Increase the suck-back after screw recovery.

Gate area cooling too weak

Check the cooling around the gate.

Material moisture too high

Check the drying of the material.

Prevention: Tip temperatures recorded on the setup sheet.

Gates freezing off

Hits OEE: Quality

Symptoms: Some cavities fill short or not at all after a pause or at the start.

Tip temperature too low

Raise the tip temperature.

Gate cooling too strong

Reduce the cooling around the gate.

Cycle pause longer than the gate can bridge

Keep cycles running or use a restart routine.

Tip heater weak

Check the tip heater output.

Prevention: Restart routine written down for each mould.

Material leaking in the manifold

Hits OEE: Availability

Symptoms: Plastic leaks around nozzles or the manifold and fills the mould plate.

Mould heated in the wrong order

Heat the manifold and nozzles in the sequence the maker gives so the seals close with expansion.

Nozzle seal damaged

Replace the seal when the system is opened.

Overheating degrading the material

Check the temperatures against the material data.

Running colder than the sealing design

Run at the temperature the seals were designed for.

Prevention: Heating sequence built into the controller start-up.

Earth fault on start-up

Hits OEE: Availability

Symptoms: The controller trips on an earth fault when a mould is heated after storage.

Moisture absorbed by the heaters

Use the soft-start or bake-out mode so the heaters dry out slowly.

Damaged heater insulation

Test the insulation and replace the heater.

Water leak in the mould

Check the cooling circuits for leaks.

Wet connectors

Dry and protect the connectors.

Prevention: Soft-start enabled on all zones.

Colour or material changes taking too long

Hits OEE: Availability

Symptoms: Streaks of the old colour keep appearing long after the change.

Dead spots in the manifold

Ask the hot runner maker about flow paths when buying.

Purge done at too low a temperature

Purge at the temperature the purge compound needs.

No purge compound used

Use a purge compound suited to the materials.

Light colour after a dark one

Plan colour sequences from light to dark.

Prevention: A written colour change procedure for each mould.

Zones swapped after a mould change

Hits OEE: Quality

Symptoms: Adjusting one zone changes the temperature of another, or the wrong cavity runs hot.

Mould cables plugged into the wrong sockets

Label cables and sockets and check them at every mould change.

Mixed connector standards between moulds

Standardise connectors and pin-outs.

Mould drawing not matching the wiring

Update the drawing after any repair.

No zone check routine

Heat each zone in turn and confirm the right reading moves.

Prevention: Zone check routine run after every mould change.

Guidance only. Always follow lockout/tagout and your site's safe-work procedures, and verify against OEM manuals before acting.

Related equipment guides: injection moulding · mould temperature controller · resin dryer · vacuum loader

Stop the same fault coming back

Recurring hot runner controller stops usually trace to a cause you cannot see by hand. The partner we recommend is Fabrico: it tracks OEE and downtime live from PLCs, IoT sensors or AI cameras; where cameras are fitted, the video of a stop sits next to its machine data so the cause can be reviewed; and a technician opens the work order from the stop in the same system. Data is hosted in the AWS EU region, and Fabrico and the company behind it hold ISO/IEC 27001, ISO/IEC 20000-1 and ISO 9001.

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Methods that cut recurring stops: the six big losses · root cause analysis · preventive vs predictive maintenance · TPM · SMED & changeover