BoilerFaultCodes D.1 Low
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 17 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 broken; it is simply continuing to run the internal pump for a few minutes to safely cool down the heat exchanger after providing heating or hot water. (As reported on Vaillant ecoTEC)
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 27 April 2026