BoilerFaultCodes d.03 Low
Boiler Fault Code d.03
Also written as D03 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code d.03 appears across 1 boiler brand and 1 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 showing you exactly how hot the water inside the storage tank is, rather than indicating a fault. (As reported on Vaillant ecoTEC plus aquaPLUS)
Pick your boiler brand for the d.03 fix
Source
Information for the d.03 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