S.02 Low

Glow-worm S.02 Fault Code

Also written as S02 — same fault.

The Glow-worm S.02 fault code means: your boiler is simply performing a routine preparation step by running its internal pump before ignition to ensure safe water flow.. It appears on 32 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: pump pre-run

What causes the Glow-worm S.02 fault?

This status occurs when the boiler detects a demand for heat and starts the internal pump to move water through the heat exchanger. It is a vital safety check designed to ensure there is sufficient water flow before the burner ignites to prevent the system from overheating. Once the electronics confirm the water is circulating correctly, the boiler will proceed to the ignition stage.

DIY fix possible

This fault may be fixable without an engineer. Check your manual first.

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Glow-worm models that show the S.02 fault code

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

Source

Glow-worm S.02 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 31 August 2026