S.01 Low

Glow-worm S.01 Fault Code

Also written as S01 — same fault.

The Glow-worm S.01 fault code means: your boiler is preparing to start the heating process by running the internal fan to clear out the combustion chamber.. It appears on 30 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: fan pre-run

What causes the Glow-worm S.01 fault?

This is not actually a fault, but rather a normal part of the boiler's starting routine where the fan spins up to clear any residual gases from the burner area. It occurs every time the system receives a request for heat or hot water to ensures the appliance is safe to ignite. If the boiler stays stuck on this code without firing up, it usually indicates the fan cannot reach the required speed or the air pressure switch isn't detecting enough airflow.

DIY fix possible

This is a normal status code, not a fault; you do not need to do anything.Wait a few moments for the boiler to complete its start-up sequence.If the code stays on screen for a long time without the boiler firing, try a simple reset.

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Glow-worm models that show the S.01 fault code

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

Source

Glow-worm S.01 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 7 July 2026