BoilerFaultCodesGlow-worm F1 Fault Code
The Glow-worm F1 fault code means: your boiler has failed to light the flame needed to provide heating or hot water, and it has now locked itself out for safety.. It appears on 24 Glow-worm models in our database.
Technical description: Ignition failure
What causes the Glow-worm F1 fault?
This fault occurs when the temperature sensor inside your hot water storage tank detects that the water has dropped to a near-freezing level. To protect the internal components from being damaged by expanding ice, the boiler temporarily pauses operation until the water temperature rises to a safe level. This is typically caused by extremely cold incoming mains water or a storage tank located in an unheated area like a garage or loft.
This fault is almost exclusively seen during the winter months when external temperatures drop significantly and reduce the temperature of the incoming mains water.
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.
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A cover plan would handle faults like F1: no call-out fees, no surprise bills.
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Glow-worm models that show the F1 fault code
Click a model for the full fault code list and model-specific repair notes.
- 18si Repair: £90-250
- 38cxi Repair: £120-250
- Ci Plus Repair: £120-300
- Ci Range Repair: £90-250
- Compact (2006-2011) Repair: £120-250
- CXi Repair: £120-250
- Flexicom 18sx Repair: £100-£350
- Flexicom cx Repair: £100-£350
- Flexicom CXi Repair: £120-250
- Flexicom hx Repair: £100-£350
- Flexicom sx Repair: £100-£350
- Glow-worm Micron 100FF 120FF Repair: £120-200
- Jaguar Combi Repair: £120-250
- Space Saver Repair: £120-220
- Space Saver 30 40 50 Repair: £100-200
- Ultimate Repair: £90-220
- Ultracom 2 CXI Repair: £100-350
- Ultracom 2 HXI Repair: £100-350
- Ultracom 2 SXI Repair: £120-250
- Ultracom 24cx 30cx Repair: £100-350
- Ultracom 35 Store Repair: £100-350
- Ultracom cxi Repair: £100-350
- Ultracom sxi Repair: £150-350
- Xtramax HE Repair: £100-350
Source
Glow-worm F1 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 7 July 2026