BoilerFaultCodesViessmann 345 Fault Code
The Viessmann 345 fault code means: the boiler has automatically shut down because it became too hot, but it will attempt to restart itself once it has cooled down.. It appears on 1 Viessmann model in our database.
Technical description: Temperature limiter has responded; burner locked out, auto re-enable after cool-down
DIY fix possible
Check that your home's thermostat is turned downEnsure all radiator valves are fully open to allow water to circulateCheck the boiler pressure gauge and top up to 1.5 bar if it is too lowWait for the boiler to cool down and see if it restarts automatically
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Viessmann models that show the 345 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Viessmann 345 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