Boiler Fault Code 1-b4

Also written as 1B4 — same fault.

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

Fault code 1-b4 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 is struggling to accurately measure the temperature of the water going to your taps, which might result in the water being too hot or too cold. (As reported on Worcester Bosch Greenstar 8000 Life/Style)