F.63 High

Vaillant F.63 Fault Code

Also written as F63 — same fault.

The Vaillant F.63 fault code means: your boiler's internal computer has encountered a critical communication error and can no longer safely control the system, meaning your heating and hot water will be unavailable until a professional technician resolves the issue.. It appears on 46 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: EMC fault EMC or electronics defect

What causes the Vaillant F.63 fault?

This fault occurs when the boiler's central control board suffers an internal memory failure, meaning it can no longer store or read the vital settings needed to operate safely. It is typically caused by the steady degradation of electronic components over time or a sudden electrical surge that corrupts the board's permanent memory. Because the boiler no longer knows its own configuration, it shuts down immediately as a safety precaution.

Typical repair cost £250-450 (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.63 fault code

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

Source

Vaillant F.63 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