b1 High

Boiler Fault Code b1

Also written as B1 — same fault.

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed

Fault code b1 appears across 2 boiler brands and 49 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler's main control chip is either loose or has failed, which means the computer can't identify the specific model to operate safely. (As reported on Worcester Bosch Greenstar 25HE)

Pick your boiler brand for the b1 fix

Viessmann b1 9 models Worcester Bosch b1 40 models

Source

Information for the b1 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