BoilerFaultCodesGlow-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 29 Glow-worm models in our database.
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.
- Betacom4
- Compact
- Easicom 24 Repair: £120-250
- Easicom 28 Repair: £120-250
- Easicom3 Combi
- Easicom3 System
- Energy
- Energy Regular
- Energy System
- Energy7 Combi
- Energy7 Regular
- Energy7 System
- Essential
- Flexicom 18sx
- Flexicom 24c / 28c
- Flexicom 30sx
- 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 35 Store
- Ultracom 38cxi
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