Troubleshooting / Mould temperature controller

Mould Temperature Controller Troubleshooting

The most common mould temperature controller problems on the plant floor, with the likely causes and the fix for each. Part of the OEE Lab troubleshooting directory.

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Problems on this page:

Mould not reaching temperatureTemperature overshoot or swingingLow flow alarmLeaks at hoses and couplingsPump noise or cavitationScale and corrosion in the circuitOver-temperature safety tripParts warping or sink marks from uneven mould temperatureHeat transfer oil degradingMould cooling too slowly

Mould not reaching temperature

Hits OEE: Availability

Symptoms: The unit takes too long to heat the mould, or never reaches the setpoint.

Heater element failed
Check the elements and their contactor.
Flow through the mould too low
Check the hoses, couplings and channels for blockage.
Scale in the mould channels
Descale the channels and treat the water.
Unit too small for the mould
Check the heating capacity against the mould.

Prevention: Heat-up time recorded at each mould change.

Temperature overshoot or swinging

Hits OEE: Quality

Symptoms: Mould temperature swings around the setpoint and part quality varies.

Control loop badly tuned
Run the auto-tune or set the loop for the mould.
Cooling valve sticking
Clean or replace the cooling valve.
Sensor in the wrong place
Use the sensor position that reflects the mould temperature.

Prevention: Mould temperature trended with the moulding process data.

Low flow alarm

Hits OEE: Availability

Symptoms: The unit stops on low flow.

Blocked mould channel
Flush the channels and check the flow per circuit.
Valve closed or hose kinked
Check the circuit valves and hose routing.
Pump wear
Check the pump and its impeller.

Prevention: Flow per circuit checked at mould setup.

Leaks at hoses and couplings

Hits OEE: Availability

Symptoms: Water or oil leaks at the mould connections.

Coupling seals worn
Replace the coupling seals.
Hoses aged by heat
Replace hoses rated for the temperature.
Couplings not fully engaged
Check the couplings at every mould change.

Prevention: Hose and coupling inspection at each mould change.

Pump noise or cavitation

Hits OEE: Availability

Symptoms: The pump rattles and the flow becomes unstable.

Low fluid level
Top up and find the leak.
Air in the system
Vent the system.
Water too close to boiling for the system pressure
Use a pressurised unit or lower the temperature.

Prevention: Fluid level checked daily.

Scale and corrosion in the circuit

Hits OEE: Quality

Symptoms: Flow falls over time and the mould heats unevenly.

Untreated hard water
Use treated water and check it regularly.
Corrosion inhibitor missing
Dose the inhibitor the water treatment supplier specifies.
Mixed metals in the circuit
Review the materials of fittings.

Prevention: Water quality checks on the cooling and heating circuits.

Over-temperature safety trip

Hits OEE: Availability

Symptoms: The unit shuts down on its safety thermostat.

Control sensor faulty
Replace the sensor.
Heater contactor welded closed
Replace the contactor.
No flow through the heater
Fix the flow problem before reset.

Prevention: Safety thermostat tested at the annual service.

Parts warping or sink marks from uneven mould temperature

Hits OEE: Quality

Symptoms: Parts warp or show sink marks that change with mould temperature.

Temperature difference between mould halves
Check each half and balance the circuits.
One circuit with low flow
Measure flow per circuit and clear the blocked one.
Setpoint not matched to the material
Use the mould temperature the material supplier recommends.

Prevention: Mould surface temperatures checked at setup.

Heat transfer oil degrading

Hits OEE: Availability

Symptoms: The oil darkens, smells burnt, and deposits build up in the heater and mould channels.

Oil running above its rated temperature
Keep the setpoint within the oil maker limit and check the safety thermostat.
Oil in contact with air in an open expansion tank
Check the expansion tank and use a closed or blanketed system where the maker allows.
Oil past its service life
Test the oil and change it when the results say so.
Mixed oil types after top-ups
Top up only with the same oil grade.

Prevention: Oil samples tested at the interval the oil supplier recommends.

Mould cooling too slowly

Hits OEE: Availability

Symptoms: The mould takes too long to come down to temperature after a setpoint change or at the end of a run.

Cooling water supply too warm
Check the central chiller or cooling tower supply temperature.
Cooling water flow too low
Check the supply valves, strainers and pressure difference.
Internal heat exchanger scaled
Descale the exchanger and treat the cooling water.
Cooling valve not opening fully
Check the valve and its control output.

Prevention: Cooling water supply temperature and pressure checked on the weekly round.

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 · chiller · resin dryer · blow moulding machine · extruder · hot runner controller

Stop the same fault coming back

Recurring mould temperature 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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Related tools: full troubleshooting directory · OEE calculator · downtime cost · MTBF / MTTR · glossary

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