366 Emergency

Viessmann 366 Fault Code

The Viessmann 366 fault code means: your boiler has detected an internal electrical safety issue where the gas valve remains powered when it should be shut off.. It appears on 1 Viessmann model in our database.

Act immediately

Turn off your boiler and stop using gas appliances. Call a Gas Safe engineer now. This fault can be dangerous if ignored.

Technical description: Gas valve electricity supply does not turn off
Typical repair cost £350-£650 (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 366 fault code

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

Source

Viessmann 366 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