d.16 Low

Glow-worm d.16 Fault Code

Also written as D16 — same fault.

The Glow-worm d.16 fault code means: your boiler is currently receiving a signal from your wall thermostat indicating that it is being told to turn on, which is normal operation rather than a fault.. It appears on 6 Glow-worm models in our database.

Monitor it

This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.

Technical description: Status of the 24V room thermostat

DIY fix possible

Check your wall thermostat to see if it is set to 'on' or 'heating demand'.Turn the temperature setting on your wall thermostat down to see if the status code changes.If the code persists while the heating is off, consult your thermostat manual for wiring or battery issues.

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Glow-worm models that show the d.16 fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Glow-worm d.16 fault code information on this page is sourced and cross-checked against the official Glow-worm service / installation manuals for each affected model.

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