Boiler Fault Code F.545

Also written as F545 — same fault.

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

Fault code F.545 appears across 1 boiler brand and 4 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning A sensor that monitors the temperature for your second heating zone (such as underfloor heating) has developed an electrical fault, causing your boiler to close the mixing valve to prevent overheating. (As reported on Viessmann Vitodens 222-F B2TF)