F.65 High

Vaillant F.65 Fault Code

Also written as F65 — same fault.

The Vaillant F.65 fault code means: your boiler's internal computer is overheating, which has caused the system to shut down to prevent damage to the electronics.. It appears on 53 Vaillant models in our database.

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description: PCB processor temperature too high | Check earth connection or electronics defect

What causes the Vaillant F.65 fault?

This fault occurs when the boiler's internal control center exceeds its safe operating temperature and shuts down to prevent the circuit board from melting or catching fire. It is usually caused by an electrical component failing on the board itself or excessive heat building up inside the boiler casing due to poor ventilation. In some cases, external heat source interference or a maturing electronic component can cause this overheating.

This fault is more common during the summer months or during heatwaves, as high ambient temperatures make it harder for the internal electronics to shed heat.

Typical repair cost £280-450 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Vaillant models that show the F.65 fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Vaillant F.65 fault code information on this page is sourced and cross-checked against the official Vaillant service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026