BoilerFaultCodes D.040 Low
Boiler Fault Code D.040
Also written as D040 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code D.040 appears across 1 boiler brand and 7 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.
Most common meaning Your boiler is measuring the temperature of the water flowing through it, but this code is just a status update indicating the current heat level rather than a fault. (As reported on Vaillant ecoTEC Pro 24)
Pick your boiler brand for the D.040 fix
Source
Information for the D.040 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 7 July 2026