Quick answer: The Glow-worm F28 fault means ignition failure — the boiler tried to light but couldn’t establish a flame, so it locked out for safety. Common causes are gas supply problems, a frozen condensate pipe, or ignition faults. A single reset may clear it; repeated F28 lockouts need a Gas Safe engineer.
F28 leaves you without heat or hot water, so it always feels pressing. Here’s what causes it and what you can safely check yourself. Worth noting first: if your Glow-worm is over about seven years old and ignition faults like F28 keep recurring, an ageing boiler is often better replaced than repeatedly repaired — a new gas boiler installed in Edinburgh can be the more economical choice.
What Does the Glow-worm F28 Error Code Mean?
F28 means the boiler failed to ignite — it tried to fire but no flame was established, so it shut down.
Rather than keep releasing gas without lighting it, the boiler locks out. It’s the safety system working correctly, but something stopped ignition.
What Causes a Glow-worm F28 Ignition Fault?
The usual causes are gas supply issues, a frozen condensate pipe, or ignition and gas valve faults.
- Gas supply — an off or partly closed valve, or low pressure
- Frozen condensate pipe — very common in Scottish winters
- Ignition electrodes or leads — worn, so no spark
- Gas valve fault — not delivering gas correctly
- Empty LPG tank — if you’re not on mains gas
How Do You Fix a Glow-worm F28 Error?
Check your gas is on and other appliances work, look for a frozen condensate pipe, then reset once.
- Test other gas appliances — if none work, it’s a supply issue
- Check the gas valve to the boiler is fully open
- Check the condensate pipe for freezing if it’s cold (see below)
- Reset once using the reset button
If F28 returns immediately, stop and book a boiler repair — the ignition system needs an engineer.
Can a Frozen Condensate Pipe Cause Glow-worm F28 in Scotland?
Yes — a frozen condensate pipe is one of the most common winter triggers for an F28 lockout here, and thawing it is usually a safe DIY step.
When the outdoor condensate pipe freezes, waste water backs up and the boiler locks out. Gently warming the exposed outdoor section with warm water or a covered hot water bottle usually clears it, then a reset should restore heat. Given our winters, always check this first.
Does Servicing Prevent F28 Faults?
Yes — servicing keeps the ignition electrodes, gas valve and condensate system healthy, heading off many F28 lockouts.
A yearly boiler service is the best defence against surprise ignition faults, and an autumn slot means your boiler is ready for the cold when F28 is most likely.
When Should You Call an Engineer for Glow-worm F28?
Call a Gas Safe engineer if the boiler won’t ignite after a reset, if other gas appliances fail too, or if you suspect an ignition or gas valve fault.
Ignition and gas components are engineer-only. If the simple checks don’t clear it, call.
Local Glow-worm Boiler Repairs Across Edinburgh and Scotland
Being Edinburgh-based and covering central Scotland means we can reach a no-heat F28 fast — and we see plenty each winter. If your Glow-worm won’t fire, contact our Gas Safe engineers.
Frequently Asked Questions About the Glow-worm F28 Error
What’s the difference between the Glow-worm F28 and F22 codes?
F28 is an ignition failure, while the Glow-worm F22 error is a low water pressure fault. If your pressure is fine but the boiler won’t light, F28 is about gas supply and ignition, not pressure.
Could an F75 fault be linked to my F28?
They’re separate issues — the Glow-worm F75 error is a pump or sensor fault, whereas F28 is ignition. But a boiler with multiple faults is worth having fully checked rather than treated code by code.
How many times should I reset my Glow-worm after F28?
Once. If it won’t ignite after a single reset, further resets won’t help, and it’s time for a Gas Safe engineer.
Why is my Glow-worm showing F28 in cold weather?
Frozen condensate pipes are a leading winter cause of F28 in Scotland. Thawing the exposed outdoor pipe often clears the fault after a reset.
