Boiler Fault Code b7 (257)

Also written as B7257 — same fault.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026

Fault code b7 (257) appears across 1 boiler brand and 4 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler's internal computer is malfunctioning and cannot communicate with the rest of the unit to operate your heating or hot water. (As reported on Worcester Bosch Greenstar 12i System)