S.04 Low

Heatline S.04 Fault Code

Also written as S04 — same fault.

The Heatline S.04 fault code means: your boiler is simply letting you know that the burner is currently lit and the system is working as it should to provide heating or hot water.. 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: Burner lit
Typical repair cost £0 (including labour)

DIY fix possible

No action is required as this is a normal status message and not a fault.Wait for the boiler to finish its current heating cycle.Check your thermostat if you believe the heating should be off.

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Heatline models that show the S.04 fault code

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

Source

Heatline S.04 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