Gas Safe: Gas work, flue work, and PCB replacement on a gas boiler must be carried out by a Gas Safe registered engineer. Homeowners can check obvious items such as heating pressure, condensate overflow, and whether a control is unplugged — then call an engineer.
Always confirm the part number against the boiler GC number and the installation manual before ordering.
Overview
F.65 means the PCB is too hot. Either the compartment is overheating, or the board’s own temperature sensor / electronics have failed.
Vaillant meaning: Electronic temperature fault
Possible causes
- Boiler in a hot unventilated cupboard
- Case panels / insulation trapping heat on the PCB
- Defective electronics (on-board temperature monitoring)
Possible solutions
- Let the boiler cool and reset. If it only fails after a long run in a tight cupboard, improve ventilation to BS 6798 / manufacturer clearances.
- Check nothing (pipe insulation, papers, a second appliance) is against the electronics cover.
- If F.65 returns in a cool, correctly ventilated location, replace the PCB.
Possible parts needed
- Boiler PCB
- No “ventilation part” — this is installation / siting