BoilerFaultCodesGlow-worm F.86 Fault Code
Also written as F86 — same fault.
The Glow-worm F.86 fault code means: your boiler has detected that the connection to your underfloor heating system is interrupted or a safety sensor is not reporting correctly, so it has stopped providing heat to prevent damage.. It appears on 17 Glow-worm models in our database.
Technical description: Fault: Underfloor heating contact. Underfloor heating contact open, sensor disconnected or defective
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 F.86 fault code
Click a model for the full fault code list and model-specific repair notes.
- Betacom4 Repair: £120-250
- Compact Repair: £120-250
- Easicom3 Combi Repair: £120-220
- Easicom3 System Repair: £120-250
- Energy Repair: £120-250
- Energy Regular Repair: £120-250
- Energy System Repair: £120-250
- Energy7 Combi Repair: £120-220
- Energy7 Regular Repair: £120-250
- Energy7 System Repair: £120-250
- Essential Repair: £120-250
- Flexicom 24c / 28c Repair: £120-250
- MicraCom Repair: £120-250
- Sustain 12s Repair: £90-180
- Ultimate 3 25R Repair: £120-250
- Ultimate3 Combi Repair: £120-250
- Ultimate3 System Repair: £120-250
Source
Glow-worm F.86 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 Compact manual (PDF)
- Glow-worm Easicom3 Combi manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026