BoilerFaultCodes d3 High
Boiler Fault Code d3
Also written as D3 — same fault.
Reviewed by the BoilerFaultCodes Editorial Team Last reviewed
Fault code d3 appears across 1 boiler brand and 22 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.
Most common meaning Your boiler has lost its connection to an essential safety internal plug, meaning it currently cannot communicate correctly with its control system. (As reported on Worcester Bosch Greenstar 12i System)
Pick your boiler brand for the d3 fix
Source
Information for the d3 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