BoilerFaultCodes D.(1) Emergency
Boiler Fault Code D.(1)
Also written as D1 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code D.(1) appears across 2 boiler brands and 11 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.
Most common meaning Your boiler is not turning off when the water gets hot enough, which runs the risk of the system overheating. (As reported on Potterton Kingfisher 2 RS60, RS80, RS100)
Pick your boiler brand for the D.(1) fix
Source
Information for the D.(1) 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 31 August 2026