BoilerFaultCodes D.26 High
Boiler Fault Code D.26
Also written as D26 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code D.26 appears across 1 boiler brand and 2 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 electrical issue with an internal component responsible for controlling external accessories, which may be preventing the system from operating correctly. (As reported on Vaillant ecoTEC 65kW)
Pick your boiler brand for the D.26 fix
Source
Information for the D.26 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