BoilerFaultCodes D.129 Low
Boiler Fault Code D.129
Also written as D129 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code D.129 appears across 2 boiler brands and 4 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 register the correct temperature settings for your hot water, which may lead to your taps not getting as hot as they should be. (As reported on Vaillant ecoTEC plus)
Pick your boiler brand for the D.129 fix
Source
Information for the D.129 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