BoilerFaultCodesViessmann 545 Fault Code
The Viessmann 545 fault code means: your boiler has detected a faulty connection in a temperature sensor for a secondary heating zone, so it has stopped that zone from heating to prevent potential damage.. It appears on 1 Viessmann model in our database.
Technical description: Emergency function operating mode is activated for heating circuit 2: Mixer closes. Heating circuit pump is operational. Short circuit, flow temperature sensor for heating circuit 2 with mixer
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 545 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Viessmann 545 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