BoilerFaultCodesGlow-worm S.33 Fault Code
Also written as S33 — same fault.
The Glow-worm S.33 fault code means: your boiler has detected an issue with the air pressure system needed for safe combustion and is keeping the internal fan running to clear any potentially harmful gases from the flue.. It appears on 13 Glow-worm models in our database.
Technical description: Forcedfanoperationuntilthepressuremonitorisswitched
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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.33: no call-out fees, no surprise bills.
Affiliate links. We may earn a commission at no extra cost to you.
Glow-worm models that show the S.33 fault code
Click a model for the full fault code list and model-specific repair notes.
- Betacom4 Repair: £150-300
- Easicom3 Combi
- Easicom3 System Repair: £150-300
- Energy Repair: £150-300
- Energy System Repair: £150-250
- Energy2 30c
- Energy7 Combi Repair: £150-300
- Energy7 System Repair: £150-300
- Essential Repair: £80-120
- Sustain 12s Repair: £150-300
- Ultimate 3 25R Repair: £120-250
- Ultimate3 Combi Repair: £120-250
- Ultimate3 System Repair: £150-300
Source
Glow-worm S.33 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