Boiler Fault Code 1-b3

Also written as 1B3 — same fault.

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

Fault code 1-b3 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 that the hot water is getting too hot, likely due to a sensor measurement issue or a temporary building of heat in the system. (As reported on Worcester Bosch Greenstar 8000 Life/Style)