How much does it cost to fix boiler error code d.31?

Typical repair cost for the boiler d.31 fault is £120-250 including labour.

d.31 Medium

Boiler Fault Code d.31

Also written as D31 — same fault.

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed 7 July 2026

Fault code d.31 appears across 2 boiler brands and 12 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 an issue with its internal system that automatically tops up the water pressure, meaning it may be unable to maintain the correct levels needed to function properly. (As reported on Vaillant Home Combi)

Pick your boiler brand for the d.31 fix

Glow-worm d.31 4 models Vaillant d.31 8 models

Source

Information for the d.31 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