BoilerFaultCodes D.20 Low
Boiler Fault Code D.20
Also written as D20 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code D.20 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 has reached the maximum allowed temperature for heating your hot water cylinder and is pausing operation as a standard safety limit. (As reported on Vaillant ecoTEC)
Pick your boiler brand for the D.20 fix
Source
Information for the D.20 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