BoilerFaultCodes D.166 High
Boiler Fault Code D.166
Also written as D166 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code D.166 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's internal computer is struggling to read data from its sensors, which prevents it from safely controlling your heating and hot water. (As reported on Vaillant ecoTEC Plus 832)
Pick your boiler brand for the D.166 fix
Source
Information for the D.166 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