F.402 High

Viessmann F.402 Fault Code

Also written as F402 — same fault.

The Viessmann F.402 fault code means: your boiler's main internal computer has developed a serious electronic fault and can no longer safely control the burner, meaning your heating and hot water will not work.. It appears on 4 Viessmann 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: BCU burner control unit faulty
Typical repair cost £450-£700 (including labour)

Engineer required

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

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Viessmann models that show the F.402 fault code

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

Source

Viessmann F.402 fault code information on this page is sourced and cross-checked against the official Viessmann service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026