BoilerFaultCodes F.33 High
Boiler Fault Code F.33
Also written as F33 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code F.33 appears across 2 boiler brands and 17 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 cannot confirm that harmful exhaust fumes are being safely cleared away through the flue pipe. (As reported on Vaillant Thermocompact)
Pick your boiler brand for the F.33 fix
Source
Information for the F.33 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