How much does it cost to fix Vaillant error code F.XX?

Cost varies. Contact a Gas Safe registered engineer for a quote.

F.XX High

Vaillant F.XX Fault Code

Q: What does the Vaillant F.XX fault code mean?

Your boiler has detected a general internal error that is stopping it from working properly, and it now needs a professional diagnostic assessment to identify the specific cause.

Also written as FXX — same fault.

The Vaillant F.XX fault code means: your boiler has detected a general internal error that is stopping it from working properly, and it now needs a professional diagnostic assessment to identify the specific cause.. It appears on 8 Vaillant models in our database.

Technical description: Fault codes (refer to the table in the appendix for advice)

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.XX fault code

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

Source

Vaillant F.XX 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