Boiler Fault Code LOCKOUT: a

Also written as LOCKOUTA — same fault.

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

Fault code LOCKOUT: a appears across 1 boiler brand and 2 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 has become blocked by dust or debris, preventing the main heating system from firing up. (As reported on Potterton Housewarmer)