BoilerFaultCodesHeatline d.16 Fault Code
Also written as D16 — same fault.
The Heatline d.16 fault code means: your boiler is simply reporting that it is currently receiving a signal from your wall-mounted heating controller to turn the heating on.. It appears on 2 Heatline models in our database.
Technical description: Current state of the 24V room thermostat
DIY fix possible
Check your room thermostat settings to see if it is currently requesting heatAdjust the thermostat temperature dial lower to see if the status code changesIf the boiler is working normally otherwise, no action is required as this is a status indicator rather than a fault
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Heatline models that show the d.16 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Heatline d.16 fault code information on this page is sourced and cross-checked against the official Heatline service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026