d.23 Low

Boiler Fault Code d.23

Also written as D23 — same fault.

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed

Fault code d.23 appears across 3 boiler brands and 45 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning This code is not actually an error; it is a status message showing that your boiler is currently set to 'Summer' mode, meaning it will only provide hot water and not central heating. (As reported on Vaillant Turbomax Plus VUW 242E)

Pick your boiler brand for the d.23 fix

Glow-worm d.23 6 models Heatline d.23 7 models Vaillant d.23 32 models

Source

Information for the d.23 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