b34 High

Boiler Fault Code b34

Also written as B34 — same fault.

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed

Fault code b34 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 unstable electrical supply from the national grid or your home wiring, causing it to shut down for safety. (As reported on Johnson Starley Warmcair DW)

Pick your boiler brand for the b34 fix

Johnson Starley b34 1 model

Source

Information for the b34 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