Glow-worm F32 Fault Code: Causes, Fixes & Repair Costs
What does the Glow-worm F32 fault code mean?
The F32 fault code on a Glow Worm boiler signals that the fan is not maintaining a consistent or adequate speed. Because the fan is responsible for pushing waste combustion gases safely out through the flue, any significant variation in its speed triggers an automatic lockout — the boiler shuts down as a precaution to prevent dangerous gases from remaining inside the appliance or being expelled incorrectly. You will lose both heating and hot water until the underlying issue is resolved. This fault is closely related to the same fan-speed monitoring technology used across the wider Vaillant Group range, of which Glow Worm has been a part since 2001.
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
- Faulty or worn fan motor Common
The fan motor is the most frequent culprit behind F32. Over time the motor bearings wear, the motor windings degrade, or the impeller becomes unbalanced, causing the fan to spin erratically or not reach the target speed the boiler's PCB expects to see. The boiler detects this deviation and locks out immediately.
- Blocked flue or air intake Common
A partial or full obstruction in the flue pipe — such as debris, a bird's nest, leaves, or ice during cold spells — creates back pressure that slows the fan below its required speed. Similarly, a blocked air intake starves the fan of the airflow it needs to operate correctly. Either scenario produces the same F32 response.
- Communication breakdown between fan and PCB Sometimes
Modern Glow Worm fans send speed feedback signals back to the PCB continuously. If the wiring connector between the fan and the PCB is corroded, loose, or damaged, the PCB stops receiving valid speed data and raises F32 even if the fan itself is physically fine. This is particularly noted on the Ultimate3 range.
- No or incorrect voltage reaching the fan Sometimes
If the PCB itself is failing or a wiring fault is interrupting the electrical supply, the fan may receive insufficient voltage to run at all. The boiler then sees zero fan speed and triggers a lockout. This points away from the fan as the faulty component and towards the PCB or associated wiring.
- Wet or damaged sensors Rare
Water ingress from an internal leak can reach the fan assembly or nearby sensors, causing erratic readings that mimic a fan speed fault. Damp connectors and corroded terminals in the fan circuit can produce intermittent F32 faults that come and go before eventually becoming permanent.
How to fix it
- Reset the boiler once or twice DIY safe
Switch the boiler off at the programmer or control panel, wait two to three minutes for it to fully power down, then switch it back on and attempt a reset using the boiler's reset button. Occasionally a transient voltage spike or brief obstruction can cause a one-off F32 that clears on reset. If the fault returns promptly, do not keep resetting — repeated resets on a genuine fan fault will not fix it and may mask a safety issue.
- Check the external flue terminal for obvious blockages DIY safe
Go outside and visually inspect where the flue exits the building. Look for visible debris, a bird's nest, ice build-up, or any object that may have partially covered the flue outlet. Do not insert anything into the flue. If you spot an obvious external obstruction that can be safely removed without tools or accessing the boiler itself, clear it. If the terminal is damaged or the blockage is internal, leave it for an engineer.
- Listen and look at the boiler fan area (observation only) DIY safe
With the boiler cover in place, listen when you attempt to fire the boiler. A functioning fan produces a clear, steady hum before ignition. Grinding, rattling, intermittent spinning, or complete silence from the fan area all indicate a mechanical problem. This is observational only — do not remove the boiler casing or touch any internal components.
- Have a Gas Safe engineer inspect and test the fan Gas Safe engineer
A registered engineer will remove the boiler casing safely, check for 230V supply at the fan terminals, and assess whether the fan motor itself is at fault. They will clean the fan blades of any debris and check that the impeller spins freely. If power is present but the fan does not run correctly, the fan assembly will need to be replaced.
- Have the engineer check wiring, connectors, and the PCB Gas Safe engineer
If the fan tests as mechanically sound, the engineer will inspect the wiring loom and connectors between the fan and PCB for corrosion, looseness, or damage. They will also check whether correct voltage is being supplied from the PCB. A PCB that is failing to output the correct voltage requires replacement by a qualified professional — this is not a homeowner task under any circumstances.
- Call a Gas Safe registered engineer if the fault persists or returns Gas Safe engineer
Because F32 is a safety lockout related to flue gas expulsion, it must be properly diagnosed and repaired by a Gas Safe registered engineer. You can find one at the Gas Safe Register website (gassaferegister.co.uk). Do not attempt to bypass the lockout or operate the boiler while the fault is active.
Parts you may need
- Boiler fan assembly (Glow Worm compatible) · from £95
- Fan wiring harness / connector · from £20
- PCB (printed circuit board) · from £220
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 £150–£320, depending on the underlying cause.
Frequently asked questions
Is the Glow Worm F32 fault dangerous?
Yes, it is treated as a safety fault. The fan's job is to ensure waste combustion gases — including carbon monoxide — are pushed out through the flue. If the fan is not running at the correct speed, there is a risk those gases are not expelled properly. This is precisely why the boiler locks out rather than continuing to run. Do not attempt to override the lockout. Make sure you have a working carbon monoxide alarm installed and call a Gas Safe engineer promptly.
How much does it cost to fix an F32 fault code on a Glow Worm boiler?
For most people, the repair involves replacing the fan motor, which typically costs £150–£320 all-in including parts and labour. If the fault turns out to be a blocked flue rather than a failed fan, the cost is often lower and may fall within the engineer's call-out fee. If the PCB is at fault, expect to pay considerably more — PCB replacement on a Glow Worm boiler can run to £400–£550 including labour, though this is a less common outcome for F32.
Why does my F32 fault keep coming back after a reset?
A reset only clears the lockout temporarily — it does not fix the underlying problem. If F32 returns within minutes or hours of resetting, the fan, its wiring, or the PCB has a real fault that needs hands-on diagnosis by a Gas Safe engineer. Repeatedly resetting a safety fault is not recommended and will not prevent the issue from recurring.
Which Glow Worm models are affected by F32?
The F32 code is most commonly seen on the Betacom4, Ultracom3, and Ultimate3 ranges. Because Glow Worm is part of the Vaillant Group, the underlying fan-monitoring technology is shared across several related brands, and the fault logic is broadly similar. If you are unsure whether your model is affected, check your boiler's data plate or manual for the model name.