BoilerFaultCodes D.125 Medium
Boiler Fault Code D.125
Also written as D125 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code D.125 appears across 1 boiler brand and 3 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 accurately measure the temperature of the hot water being sent to your taps, which may cause your hot water to fluctuate or stop working entirely. (As reported on Vaillant ecoTEC plus)
Pick your boiler brand for the D.125 fix
Source
Information for the D.125 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