BoilerFaultCodesGlow-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 25 Glow-worm models in our database.
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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A cover plan would handle faults like S.11: no call-out fees, no surprise bills.
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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.
- Betacom4
- Compact
- Easicom 24 Repair: £120-250
- Easicom 28 Repair: £120-250
- Easicom3 Combi
- Easicom3 System
- Energy
- Energy 35 Store Repair: £150-300
- Energy System
- Energy7 Combi
- Energy7 System
- Essential
- Flexicom 24c / 28c
- Flexicom cx
- MicraCom
- Sustain 12s
- Sustain 15s
- Sustain 18s
- Ultimate 3 25R
- Ultimate3 Combi
- Ultracom 2 CXI
- Ultracom 2 SXI
- Ultracom 24cx 30cx
- Ultracom 30cxi
- Ultracom 38cxi
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 31 August 2026