Boiler Fault Code 1-d4

Also written as 1D4 — same fault.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026

Fault code 1-d4 appears across 1 boiler brand and 8 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler is reporting a communication problem or a technical fault with your solar heating system, though your central heating should continue to work. (As reported on Worcester Bosch Greenstar 8000 Life/Style)