Boiler displays F.65, PCB temperature too high

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

Blocked ventilation around boiler, Boiler installed in overheated space, Faulty PCB temperature sensor, Internal PCB fault

Safety: Switch off power and allow the boiler to cool.

Improve ventilation: Ensure the boiler cupboard has adequate ventilation as per Vaillant installation manual. Remove stored items blocking airflow.
Check ambient temperature: If the boiler is in a very hot area (e.g. loft in summer), consider improving insulation and ventilation.
Reset: Once cooled, reset the boiler. If F.65 recurs frequently, a technician should check the PCB and temperature sensor.

Medium 3/5

Main Control PCB

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