BoilerFaultCodes b3 High
Boiler Fault Code b3
Also written as B3 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code b3 appears across 1 boiler brand and 6 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.
Most common meaning Your boiler's computer is experiencing an internal communication failure, which means the system cannot safely operate and requires professional intervention. (As reported on Worcester Bosch CDi Highflow)
Pick your boiler brand for the b3 fix
Source
Information for the b3 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