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 3 boiler brands and 30 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler is struggling to monitor the temperature of the water returning from your radiators, which may cause the system to stop working reliably. (As reported on Worcester Bosch Greenstar Ri)

Pick your boiler brand for the d1 fix

Viessmann d1 5 models Vokera d1 4 models Worcester Bosch d1 21 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 27 April 2026