Boiler Fault Code FB 365

Also written as FB365 — same fault.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026

Fault code FB 365 appears across 1 boiler brand and 11 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 a potential internal fuel leak during its safety check, which prevents it from starting up to ensure your safety. (As reported on Worcester Bosch Danesmoor)