BoilerFaultCodes F.433 High
Boiler Fault Code F.433
Also written as F433 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code F.433 appears across 1 boiler brand and 1 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.
Most common meaning Your boiler has stopped working because it is having trouble detecting the speed of the internal cooling fan, which is a key safety feature for safe combustion. (As reported on Viessmann Vitodens 100-W WB1A)
Pick your boiler brand for the F.433 fix
Source
Information for the F.433 fault code is sourced from the official service / installation manual for each model that displays it. Read more about how we source fault codes →
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026