Boiler Fault Code A.(3)

Also written as A3 — same fault.

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

Fault code A.(3) appears across 1 boiler brand and 3 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler is unable to start because the small starter flame is not lighting, likely due to a tiny blockage in the gas supply line. (As reported on Potterton Kingfisher 2 RS60, RS80, RS100)