BoilerFaultCodes F.400 High
Boiler Fault Code F.400
Also written as F400 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code F.400 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 Your boiler has detected an issue with the flame detection system, meaning it cannot confirm the burner is operating safely and has shut down to prevent gas from building up. (As reported on Viessmann Vitodens 100-W WB1A)
Pick your boiler brand for the F.400 fix
Source
Information for the F.400 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