BoilerFaultCodes 399 High
Boiler Fault Code 399
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code 399 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 detected an electrical fault within its main control sensor or the internal circuit board, preventing it from firing up safely. (As reported on Viessmann Vitodens 100-W B1GA)
Pick your boiler brand for the 399 fix
Source
Information for the 399 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