BoilerFaultCodesGlow-worm S.39 Fault Code
Also written as S39 — same fault.
The Glow-worm S.39 fault code means: your boiler has detected that the external sensor or switch connected to your underfloor heating system is currently open, which is preventing the boiler from activating that heating circuit.. It appears on 19 Glow-worm models in our database.
Technical description: Underfloorheatingcontactopen
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Glow-worm models that show the S.39 fault code
Click a model for the full fault code list and model-specific repair notes.
- Betacom4 Repair: £120-250
- Easicom3 Combi Repair: £120-250
- Easicom3 System Repair: £120-250
- Energy Repair: £100-250
- Energy 35 Store
- Energy Regular Repair: £120-250
- Energy System Repair: £100-250
- Energy2 30c
- Energy7 Combi Repair: £120-200
- Energy7 Regular Repair: £120-250
- Energy7 System Repair: £120-250
- Essential Repair: £100-250
- Flexicom 24c / 28c Repair: £100-£200
- Sustain 12s Repair: £100-250
- Ultimate 3 25R Repair: £120-250
- Ultimate3 Combi Repair: £120-250
- Ultimate3 System Repair: £100-250
- Ultracom 2 SXI
- Ultracom sxi
Source
Glow-worm S.39 fault code information on this page is sourced and cross-checked against the official Glow-worm service / installation manuals for each affected model.
- Glow-worm Betacom4 manual (PDF)
- Glow-worm Easicom3 Combi manual (PDF)
- Glow-worm Easicom3 System manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026