S.11 Low

Glow-worm S.11 Fault Code

Also written as S11 — same fault.

The Glow-worm S.11 fault code means: your boiler is performing a routine safety check by starting the fan before the burner ignites.. It appears on 9 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.11 fault?

This is a normal part of the boiler's startup sequence where the fan clears any leftover gases from the combustion chamber to ensure a safe ignition. It is not a fault, but rather a status update showing that the system is preparing the burner to fire up. If this code stays on the screen without the boiler eventually firing, it may indicate that the fan is struggling to reach the required speed.

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.11 fault code

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

Source

Glow-worm S.11 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 27 April 2026