Glow-worm F2 Fault Code: Causes, Fixes & Repair Costs
What does the Glow-worm F2 fault code mean?
The F2 fault code on Glow-Worm boilers indicates a problem with the combustion fan — the component responsible for drawing in fresh air and expelling flue gases safely out of your home. When the boiler's control board detects that the fan is not spinning at the correct speed, or has stopped working altogether, it triggers the F2 lockout as a safety measure to prevent harmful gases from accumulating. On certain older Glow-Worm models the F2 code can also relate to flame loss during operation, but across the most common current ranges (including the Flexicom, Ultracom, and Energy ranges) a fan-related fault is the primary meaning. Because the fan is critical for safe combustion, the boiler will refuse to attempt ignition until the fault is resolved.
General guidance only — not a substitute for professional advice. Any gas work must be carried out by a Gas Safe registered engineer. If you smell gas or suspect carbon monoxide, leave the property and call the National Gas Emergency line on 0800 111 999.
Common causes
- Worn or failed fan motor Common
The fan motor windings can burn out over time, or the internal bearings can degrade and seize. Either fault prevents the fan from reaching the speed the PCB expects before allowing ignition, triggering the F2 lockout. This is the single most common root cause.
- Faulty or disconnected fan wiring or connector Common
The wiring loom between the fan and the PCB can suffer from corrosion, a loose connector, or a damaged lead — especially in older boilers or those in damp utility areas. The PCB receives no speed signal and interprets this as a fan failure.
- Damaged or failed fan capacitor Sometimes
Many Glow-Worm fans use a start capacitor to help the motor reach running speed. When the capacitor degrades, the motor struggles to spin up quickly enough, causing an intermittent or permanent F2 fault.
- Flue or air-intake obstruction Sometimes
A blockage in the flue terminal or air intake — caused by a bird's nest, debris, or a collapsed flue section — can create back-pressure that prevents the fan from hitting its target speed, or can fool the pressure-sensing circuit into logging a fan fault.
- Internal water leak causing electrical damage Sometimes
A dripping heat exchanger, pump seal, or pipework joint inside the boiler can allow moisture to reach the fan motor or its control circuitry, causing intermittent operation or outright failure.
- PCB fault misreading fan speed Rare
If the PCB's fan-speed sensing circuit or the tacho (Hall effect) sensor on the fan itself fails, the board will log an F2 fault even though the fan is mechanically sound. This is less common but does occur on higher-mileage boilers.
How to fix it
- Turn the boiler off and check for any obvious safety concerns first DIY safe
Switch the boiler off at the programmer or room thermostat and let it sit for a couple of minutes. If you can smell gas at any point, do not proceed — turn off the gas at the meter, open windows and doors, avoid switches or naked flames, and call the National Gas Emergency Service on 0800 111 999 immediately.
- Attempt a single boiler reset DIY safe
Locate the reset button or turn the mode dial to the reset position as described in your user manual. Hold for the required time (usually 3 seconds) and release. If the boiler fires up normally, monitor it over the next hour. If the F2 code returns promptly, do not keep resetting — repeated resets will not cure an underlying fan fault and can mask the problem from the engineer.
- Visually inspect the flue terminal outside DIY safe
Go outside and check the boiler's flue outlet (the plastic pipe terminating on an external wall or through the roof). Look for obvious blockages such as a bird nest, large debris, or physical damage to the terminal grille. Do not attempt to dismantle the flue — simply report what you see to the engineer.
- Check that your gas supply is working normally DIY safe
Confirm that other gas appliances in the property (e.g., a gas hob) are working correctly. If nothing gas-powered is working, there may be a wider supply issue — contact your gas supplier or check whether a prepayment meter needs topping up.
- Call a Gas Safe registered engineer to diagnose and repair the fault Gas Safe engineer
All further work — removing the boiler casing, testing the fan motor and capacitor, inspecting internal wiring, checking the PCB tacho input, and replacing any components — must be carried out by a Gas Safe registered engineer. It is a legal requirement in the UK to use a registered engineer for gas appliance repairs. Ask the engineer to check the fan motor, capacitor, wiring loom, and flue integrity as part of the diagnostic visit.
Parts you may need
- Boiler fan / flue fan assembly (Glow-Worm compatible) · from £120
- Fan capacitor · from £15
- Fan wiring harness / connector · from £25
- PCB (printed circuit board) · from £280
The exact spare depends on your boiler's GC number (on the data badge). Check this against the part before buying.
Typical repair cost
Expect to pay roughly £200–£375, depending on the underlying cause.
Frequently asked questions
Can I reset my Glow-Worm boiler to clear the F2 code myself?
You can try a single reset, but it is unlikely to permanently clear an F2 fault. The code is triggered by the boiler's safety system detecting that the fan is not performing correctly, and resetting the boiler simply asks it to try again. If the underlying fault — a worn motor, failed capacitor, or loose wiring — is still present, the F2 code will return within minutes. Repeated resets without fixing the root cause are not recommended.
How much does it cost to fix a Glow-Worm F2 fault in the UK?
For most homeowners, the repair comes to somewhere between £200 and £375 including parts and labour. A straightforward fan replacement (the most common fix) typically falls in the £225–£275 range. If the problem is limited to a capacitor or wiring connector the cost can be lower, around £100–£150 for the call-out and labour. Bear in mind that if the fan fault has caused secondary damage to the PCB, costs can rise considerably — a replacement PCB alone can cost £180–£400 depending on the model.
Is the Glow-Worm F2 fault dangerous?
The boiler locks itself out precisely because the fan fault is a potential safety risk — without proper flue-gas extraction there is a risk of combustion gases, including carbon monoxide, not being safely removed. The lockout means the boiler will not fire while the fault is active, which is the correct response. You should not attempt to override or repeatedly reset the boiler. If you have any concerns about carbon monoxide, fit a CO alarm (legally required in new installations in England), ventilate the room, and call a Gas Safe engineer promptly.
Why does my Glow-Worm boiler show F2 only in cold weather?
Cold weather can thicken the lubricant in ageing fan bearings, making the motor sluggish to reach operating speed on start-up — which can trigger an F2 fault intermittently in winter even when the fan works fine in warmer months. This is a warning sign that the fan is nearing the end of its life and should be inspected before it fails completely, leaving you without heating or hot water during a cold snap.