Boiler Fault Code LOCKOUT: c

Also written as LOCKOUTC — same fault.

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

Fault code LOCKOUT: c 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 heater has shut down because it cannot pull in enough fresh air to operate safely, which increases the risk of dangerous carbon monoxide buildup. (As reported on Potterton Housewarmer)