Termet Fan Overrun / Stuck Relay or Sensor Misread

Boiler fan runs continuously even when there is no demand for heating or hot water.

Safety Warning

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

Possible Causes

Stuck fan relay on Termet PCB, Faulty flue temperature sensor reporting high temperature, Software fault in PCB, Incorrect wiring causing permanent fan demand

How to Fix / Troubleshooting

User checks:

Check that there is no active demand from the room thermostat or hot water taps.
Turn the boiler off at the mains; if the fan stops and restarts immediately when powered, a control fault is likely.

Technician checks:

Measure the signal from the flue temperature sensor and replace if misreading.
Inspect the PCB for a stuck fan relay and replace the board if necessary.
Verify that external controls are wired correctly and not back-feeding a demand signal.

Continuous fan operation wastes energy and may indicate a safety-related sensor issue.

Repair Difficulty

Hard 4/5

Required Part

Main Control PCB

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