BoilerFaultCodes D.026 Medium
Boiler Fault Code D.026
Also written as D026 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code D.026 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 has detected an issue with an internal electrical switch that controls optional accessories, which may prevent your heating or hot water from turning on correctly. (As reported on Vaillant ecoTEC plus)
Pick your boiler brand for the D.026 fix
Source
Information for the D.026 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