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Glow-worm Boiler Fault Codes — Wokingham
Betacom, Energy, Ultimate & Flexicom — F75, F22, F28, F29, F9 & more explained plainly
Your Glow-worm boiler has locked out to protect itself. This guide covers every common fault code across the Betacom, Energy and Ultimate ranges — what each means, what you can safely try yourself, and when to call a Gas Safe engineer. Thermotec carries genuine Glow-worm spares on the van for a single-visit fix in most cases.
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First-time
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fix rate
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Boiler showing a fault code?
Fixed price · Genuine parts · Glow-worm specialist
Diagnostic fee£96
First-time fix90%
ResponseSame day
Fault code index
Glow-worm fault codes — full reference
Find your code below. Severity indicates whether you can try a fix yourself (Low) or whether a Gas Safe engineer is required (High/Medium).
| Code | Fault | Common cause | Action | Severity |
|---|---|---|---|---|
| F75 | Pump / pressure sensor fault | Pump seized or not detected on startup; pressure sensor blocked with magnetite sludge | Top up to 1.5 bar, press Reset. If it returns, engineer needed — see dedicated F75 guide. | High |
| F28 | Ignition failure | Gas supply issue, frozen condensate pipe, faulty spark electrode or gas valve | Check gas supply. Thaw condensate pipe in winter. Press Reset 3 sec. If it returns, engineer required. | High |
| F29 | Flame loss during operation | Flame established then lost — gas valve, ionisation sensor or combustion fault | Press Reset once. If fault returns immediately, do not keep resetting — engineer diagnosis needed. | High |
| F32 | Fan fault | Fan motor failure or flue obstruction — prevents safe venting of combustion gases | Do not reset. Harmful gases cannot be vented safely. Gas Safe engineer required immediately. | High |
| F22 | Low water pressure | Pressure below safety limit — bleeding radiators, slow leak, failing expansion vessel | Repressurise to 1.5 bar using filling loop. If pressure keeps dropping, engineer needed to find leak. | Medium |
| F9 | Circulation / pressure sensor fault | Low system pressure, closed valves, or pressure sensor blocked with sludge | Check pressure — top up to 1.5 bar. Check all radiator and isolation valves are open. If F9 remains, sensor blocked — engineer needed. | Medium |
| F1 / F4 | Ignition lockout (5 attempts) | No flame after 5 attempts — gas supply, frozen condensate or faulty ignition leads | Check gas meter credit. Thaw condensate if winter. Press Reset 3 sec. If recurring, ignition leads or gas valve need inspection. | Medium |
| F24 | Overtemperature / flow temperature fault | Blocked heat exchanger, low flow, pump fault or sludge restriction | Do not keep resetting. Linked to kettling noise. Powerflush recommended to clear heat exchanger. Engineer inspection required. | Medium |
| F27 | Flame detected without demand | Gas valve fault — gas is present when the boiler hasn’t called for heat | Turn boiler off at wall. Do not restart. Gas Safe engineer required — this is a safety-critical fault. | High |
Stuart’s pro tip — the most common winter call-out in Wokingham
The F28 caused by a frozen condensate pipe is the most common Glow-worm fault we attend in winter across RG40. The white plastic pipe that exits the wall behind your boiler can freeze overnight. Before calling an engineer, locate it and pour warm — not boiling — water along it to thaw. Then press and hold the Reset button for 3 seconds. This clears the fault at no cost in the majority of winter call-outs.
Step-by-step fixes
Common Glow-worm faults — what to try first
Work through these before calling an engineer. Some faults have a genuine DIY fix — others are clear signals to stop and call immediately.
F75 — Wokingham’s most reported Glow-worm fault
The F75 is the fault code we see most on Glow-worm boilers across RG40. The boiler can’t confirm the pump is running on startup — usually because the pressure sensor is blocked with magnetite sludge, or the pump has seized. In Wokingham’s hard water area this is particularly common. We carry genuine Glow-worm pressure sensors on the van for a same-visit fix in most cases. We also recommend a magnetic filter to prevent recurrence. We have a full dedicated guide covering every cause and every fix.
Read the full F75 specialist guide →
F28 / F29
Ignition failure & flame loss
What it means
F28: the boiler tried to ignite and failed. F29: flame was established then cut out. Both are gas or flame faults — the most common winter cause is a frozen condensate pipe.
Try this first
1
Check your gas meter credit and confirm supply is live (try a gas hob).2
In winter: find the white plastic condensate pipe exiting the wall. Pour warm (not boiling) water over it to thaw.3
Press and hold the Reset button (flame symbol) for 3 seconds.If the fault returns immediately — stop resetting. Book a diagnostic →
F22
Low water pressure
What it means
Pressure has dropped below the safety minimum. The boiler has shut down to prevent the heat exchanger overheating without water — a “dry fire” situation.
Try this first
1
Find the filling loop — a silver braided hose with lever handles under the boiler.2
Slowly turn the handle(s) until the gauge reads 1.5 bar, then close them fully.3
If the code doesn’t clear, press Reset for 3 seconds.Topping up more than once a month? Hidden leak or expansion vessel fault — book a repair →
F9
Circulation / pressure sensor fault
What it means
The boiler can’t sense water moving correctly — a communication error between pump and pressure sensor. Often caused by sludge blocking the sensor, or low pressure.
Try this first
1
Check gauge — if below 1.0 bar, top up to 1.5 bar using the filling loop.2
Check all radiator TRVs and isolation valves under the boiler are fully open.3
Cycle the power off and back on at the wall switch.F9 persisting with correct pressure? Sensor blocked with sludge — book a diagnostic → or consider a powerflush →
F24
Overtemperature / kettling
What it means
Flow temperature exceeded the safety limit. Usually caused by limescale or sludge in the heat exchanger restricting water flow — linked to the “kettling” noise. Wokingham’s hard water makes this particularly common.
What to do
Do not keep resetting — the restriction will cause long-term heat exchanger damage. A professional powerflush is the correct fix. Adding a magnetic filter prevents recurrence.
F27
Flame detected without demand
What it means
Gas is detected burning when the boiler hasn’t asked for heat — a gas valve fault. This is a safety-critical fault that must be treated seriously.
What to do
Turn the boiler off at the wall immediately. Do not restart it. Call a Gas Safe engineer. If you smell gas, call the National Gas Emergency line on 0800 111 999 first.
F32
Fan fault
What it means
The fan is not running at the correct speed — or at all. The fan vents combustion gases safely through the flue. Without it working correctly, harmful gases including carbon monoxide could build up.
What to do
Do not reset repeatedly. Gas Safe engineer required to inspect the fan motor, capacitor and flue for obstructions before the boiler is used again.
Common questions
Glow-worm fault code FAQ
What do F28 and F29 mean on my Glow-worm boiler?
F28 and F29 are the most common errors on Glow-worm Energy and Ultimate models. F28 means the boiler tried to ignite and failed. F29 means the flame was established then lost during operation. In the Wokingham area, a blocked condensate pipe in winter is the most frequent cause — check this before calling an engineer. Also check your gas meter hasn’t been accidentally shut off. If the fault persists after a reset, the ignition electrode, gas valve or flame sensor is likely faulty.
How do I fix the F22 low pressure fault on my Glow-worm?
Locate the filling loop — usually a silver braided hose with blue or black lever handles underneath the boiler. Slowly open the valves until the pressure gauge reads 1.5 bar, then close them fully. The F22 code should clear automatically, or press Reset for 3 seconds. If you’re topping up more than once or twice a year, you likely have a hidden leak or a failing expansion vessel — book a diagnostic to find the root cause.
Why is my Glow-worm making a kettling or banging noise?
A kettling noise is almost always limescale or magnetite sludge in the heat exchanger restricting water flow — linked to F75 and F24 faults. The water locally overheats and creates a boiling sound. Wokingham sits in a hard water area, making this particularly common. A professional powerflush clears the debris. Adding a magnetic filter prevents it recurring.
Can I reset my Glow-worm boiler myself?
Yes. Look for the button with a flame symbol with a line through it, or a button marked “Reset.” Press and hold for 3 seconds. If the boiler locks out immediately again, stop resetting — repeatedly forcing ignition can damage the PCB or burner. One reset attempt is fine; a second should prompt a call to a Gas Safe engineer.
How often should I service my Glow-worm to keep the warranty valid?
Annually. A Gas Safe registered engineer must carry out the annual service to keep your Glow-worm manufacturer warranty valid (up to 10 years on some models). At a Thermotec service we clean the burner, check the expansion vessel, test flue gases and inspect the pressure sensor — the components most likely to cause F75, F28 and F9 faults. See our annual boiler servicing page.
Is the F75 on my Glow-worm a major repair?
Not usually. The F75 typically means the pressure sensor can’t confirm the pump is running — either because the sensor is blocked with sludge, or the pump has seized. We carry genuine Glow-worm pressure sensors on the van for a same-visit fix in most cases. If the pump itself has seized, that’s a larger job but still a standard repair. Read our dedicated F75 specialist guide for full detail on every cause and fix.
Related pages
More Glow-worm & boiler support
Glow-worm fault won’t clear? Call Stuart.
Gas Safe 599015 · £96 fixed diagnostic · 90% first-time fix · Genuine parts · F75 specialists · Same-day where available · Wokingham & RG40