BoilerFaultCodes F.77 High
Boiler Fault Code F.77
Also written as F77 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code F.77 appears across 2 boiler brands and 41 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.
Most common meaning Your boiler has detected an issue with the drainage system that removes leftover liquid from the exhaust pipe or a fault with the safety flap inside the flue. (As reported on Vaillant ecoTEC Pro / ecoTEC Plus)
Pick your boiler brand for the F.77 fix
Source
Information for the F.77 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 27 April 2026