d1 High

Boiler Fault Code d1

Also written as D1 — same fault.

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed

Fault code d1 appears across 6 boiler brands and 24 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler has stopped working because the waste water pipe is blocked, likely by debris or ice if it is cold outside. (As reported on Vokera Synergy E)

Pick your boiler brand for the d1 fix

Alpha d1 9 models Ferroli d1 1 model Gledhill d1 1 model Viessmann d1 1 model Vokera d1 5 models Worcester Bosch d1 7 models

Source

Information for the d1 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