F.41 High

Vaillant F.41 Fault Code

Also written as F41 — same fault.

The Vaillant F.41 fault code means: your boiler has lost its memory regarding the type of gas it uses and needs to be reconfigured by a professional to operate safely.. It appears on 9 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: (837/637 only) | No setting for the type of gas is stored | Set gas type in PCB (see page 30)

What causes the Vaillant F.41 fault?

This fault occurs when the boiler's internal computer suffers a data loss and can no longer identify which fuel source it should be burning. The most common reason is that the main control board has developed an electrical defect or has been replaced without the necessary configuration codes being entered. Without this specific profile, the boiler will not fire up because it cannot guarantee a safe combustion process.

Typical repair cost £90-180 (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.41 fault code

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

Source

Vaillant F.41 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 7 July 2026