BoilerFaultCodes D.27 Medium
Boiler Fault Code D.27
Also written as D27 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code D.27 appears across 1 boiler brand and 25 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 control board is having trouble communicating with an external part or accessory, which may prevent the system from starting up correctly. (As reported on Vaillant ecoTEC)
Pick your boiler brand for the D.27 fix
Source
Information for the D.27 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 27 April 2026