BoilerFaultCodes d20 High
Boiler Fault Code d20
Also written as D20 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code d20 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 encountered an undefined system error that is not documented by the manufacturer, which usually suggests a software glitch or a communication failure within the control board. (As reported on Alpha E-Tec Plus 10 / 18)
Pick your boiler brand for the d20 fix
Source
Information for the d20 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