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 run the hot water only, meaning your central heating is temporarily disabled by the user settings.. 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
Typical repair cost £0 (including labour)

DIY fix possible

Locate the mode selector button or knob on the control panelSwitch the setting from 'Hot Water Only' (Summer Mode) to 'Heating and Hot Water' (Winter Mode)Check that your room thermostat is turned up to call for heat

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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 7 July 2026