Boiler Fault Code (D) LED turning on

Also written as DLEDTURNINGON — same fault.

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

Fault code (D) LED turning on appears across 1 boiler brand and 2 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 pressure is too low to operate safely and has shut itself down as a precaution. (As reported on Ariston Genus 15 RFFI)