How much does it cost to fix boiler error code d.25?

Typical repair cost for the boiler d.25 fault is £120-220 including labour.

d.25 Low

Boiler Fault Code d.25

Also written as D25 — same fault.

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed 31 August 2026

Fault code d.25 appears across 2 boiler brands and 36 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler is currently reporting that the internal hot water pre-heating feature is not responding correctly, though this usually does not prevent the boiler from providing heating or hot water on demand. (As reported on Vaillant Turbomax Plus)

Pick your boiler brand for the d.25 fix

Glow-worm d.25 4 models Vaillant d.25 32 models

Source

Information for the d.25 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 31 August 2026