BoilerFaultCodes D.25 Low
Boiler Fault Code D.25
Also written as D25 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code D.25 appears across 1 boiler brand and 28 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.
Most common meaning Your boiler is currently busy heating your hot water because your smart thermostat or external controller has told it to do so. (As reported on Vaillant ecoTEC)
Pick your boiler brand for the D.25 fix
Source
Information for the D.25 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