Boiler Fault Code B(3)

Also written as B3 — same fault.

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

Fault code B(3) appears across 2 boiler brands and 5 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler's small starter flame is either too weak or not staying lit, which is preventing the main burner from firing up to provide heat. (As reported on Potterton Flamingo RS40 RS50)