BoilerFaultCodes D.039 Low
Boiler Fault Code D.039
Also written as D039 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code D.039 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 struggling to read the temperature from your solar water heating system, meaning it cannot accurately tell if your stored solar water is hot enough to use. (As reported on Vaillant ecoTEC Pro)
Pick your boiler brand for the D.039 fix
Source
Information for the D.039 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