Boiler Fault Code d9

Also written as D9 — same fault.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026

Fault code d9 appears across 2 boiler brands and 10 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler has detected that the water inside is heating up too quickly or is struggling to circulate, so it has safely shut itself down to prevent internal damage. (As reported on Remeha Avanta)