BoilerFaultCodes d.39 Low
Boiler Fault Code d.39
Also written as D39 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code d.39 appears across 1 boiler brand and 14 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.
Most common meaning Your boiler is simply reporting the current temperature reading from your solar heating system, which is a routine data check rather than a system error. (As reported on Vaillant ecoTEC plus System)
Pick your boiler brand for the d.39 fix
Source
Information for the d.39 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