BoilerFaultCodesGlow-worm S.91 Fault Code
Also written as S91 — same fault.
The Glow-worm S.91 fault code means: your boiler has been accidentally set to a display-only mode typically used in showrooms, meaning it will show lights and text on the screen but will not actually heat your water or radiators.. It appears on 20 Glow-worm models in our database.
Technical description: The exhibition mode is activated.
DIY fix possible
Locate the installer or user menu on your boiler's control panel.Navigate to the settings or configuration area.Find the 'Exhibition Mode' or 'Demo Mode' setting and switch it to 'Off'.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Avoid the next call-out bill
A cover plan would handle faults like S.91: no call-out fees, no surprise bills.
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Glow-worm models that show the S.91 fault code
Click a model for the full fault code list and model-specific repair notes.
- Betacom4
- Compact
- Easicom 2 24c
- EASICOM 3 25r
- Easicom3 Combi Repair: £80-120
- Easicom3 System Repair: £80-150
- Energy Repair: £0-£100
- Energy Regular Repair: £80-120
- Energy System Repair: £80-150
- Energy7 Combi Repair: £80-120
- Energy7 Regular Repair: £80-150
- Energy7 System
- Essential Repair: £80-150
- Flexicom 24c / 28c Repair: £80-120
- MicraCom Repair: £80-120
- Sustain 12s Repair: £80-150
- Sustain 15s Repair: £80-150
- Sustain 18s Repair: £80-150
- Ultimate 3 25R Repair: £80-150
- Ultimate3 Combi Repair: £80-150
Source
Glow-worm S.91 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