BoilerFaultCodes LOCKOUT: d Emergency
Boiler Fault Code LOCKOUT: d
Also written as LOCKOUTD — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code LOCKOUT: d 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 has shut down because the exhaust fumes are not being cleared away safely through the chimney or flue. (As reported on Potterton Housewarmer)
Pick your boiler brand for the LOCKOUT: d fix
Source
Information for the LOCKOUT: d fault code is sourced from the official service / installation manual for each model that displays it. Read more about how we source fault codes →
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026