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 4 boiler brands and 42 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 external safety device or a plug-in controller, causing it to stop running as a safety precaution. (As reported on Worcester Bosch Greenstar 25HE)

Pick your boiler brand for the d3 fix

Alpha d3 8 models British Gas d3 1 model Ferroli d3 2 models Worcester Bosch d3 31 models

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 31 August 2026