S.31 Low

Heatline S.31 Fault Code

Also written as S31 — same fault.

The Heatline S.31 fault code means: your boiler is currently set to only provide hot water and is ignoring requests for central heating.. It appears on 8 Heatline 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: "Hot water only" mode

DIY fix possible

Check your external timer or programmer to see if it is currently set to 'Hot Water Only' or 'Summer Mode'.Ensure your room thermostat or smart controller is set to a temperature higher than the current room temperature.Adjust the boiler's internal winter/summer settings via the control panel to enable heating mode.

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Heatline models that show the S.31 fault code

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

Source

Heatline S.31 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 27 April 2026