Boiler Fault Code D.031

Also written as D031 — same fault.

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

Fault code D.031 appears across 1 boiler brand and 3 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 automatically top up its own water pressure levels, which usually happens because the system detects a leak or the filling device has become stuck. (As reported on Vaillant ecoTEC Plus 836)