Glow-worm F28 Fault
What the F28 code on a Glow-worm boiler means — an ignition failure — the common causes, what you can safely check, and when to call a Gas Safe engineer. Call 07927 882561.
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Upfront cost — no obligation F28 on a Glow-worm boiler is an ignition failure — the boiler tried to light, no flame was detected, and it locked out to keep you safe. Glow-worm is part of the same group as Vaillant and shares its F-code system, so F28 behaves much like the Vaillant version. Some causes are simple to check; an ignition fault itself needs a Gas Safe engineer. Gas First are Gas Safe registered (587401) Glow-worm engineers across East London — here’s what F28 means and what to do.
What the F28 code means
F28 is an ignition-failure lockout: the burner has tried to light, no flame has been detected, and the boiler has shut down as a safety measure. It is a lockout, not a fault to force through by holding reset — if there’s no flame, resetting just repeats the same failed ignition. The code points at the gas, ignition or flame-sensing side of the boiler. Glow-worm also uses F1 and F22 for low water pressure (usually a DIY re-pressurise — see low boiler pressure); the full list is in our boiler fault codes guide.
F28 is an ignition-failure lockout: the burner has tried to light, no flame has been detected, and the boiler has shut down as a safety measure.
Common causes of F28
In cold weather, F28 is very often a frozen condensate pipe — the external pipe freezes and backs up, stopping the boiler firing. Otherwise the usual causes are a gas-supply problem (a gas meter that’s off, an empty prepayment meter, or a supply issue — check whether your other gas appliances work) or a fault on the ignition side: the ignition electrode, the flame-sensing electrode, or the gas valve. Because Glow-worm shares Vaillant’s code system, the same fault on a Vaillant shows F28 too — see our Vaillant F28 fault guide.
In cold weather, F28 is very often a frozen condensate pipe — the external pipe freezes and backs up, stopping the boiler firing.
What you can safely check yourself
Two checks are safe. First, make sure the gas is on — if your gas hob or another gas appliance also won’t work, it’s a supply issue rather than the boiler (check the meter and, on a prepayment meter, the credit). Second, in cold weather, check whether the external condensate pipe has frozen and thaw it gently with warm (not boiling) water. Then reset the boiler once, following the manual. If F28 comes straight back, stop resetting and call an engineer — repeated resets on a no-flame fault won’t fix it and aren’t a good idea.
Two checks are safe. First, make sure the gas is on — if your gas hob or another gas appliance also won’t work, it’s a supply issue rather…
When to call us — and how we fix it
If it isn’t the gas supply and isn’t a frozen condensate pipe, F28 needs a Gas Safe engineer. We test the ignition and flame-sensing electrodes, check the gas valve and gas pressure, and inspect the burner, then repair the actual cause so the boiler fires reliably again — with a clear price agreed before any work. We fix F28 and every other Glow-worm lockout as Glow-worm engineers across East London, from our Bow and Dagenham bases.
If it isn’t the gas supply and isn’t a frozen condensate pipe, F28 needs a Gas Safe engineer.
Frequently Asked Questions
What does F28 mean on a Glow-worm boiler?
It's an ignition-failure lockout — the boiler tried to light, no flame was detected, and it shut down safely. It points to the gas, ignition or flame-sensing side.
Can I fix a Glow-worm F28 myself?
Sometimes. Check your gas is on (do other appliances work?) and, in winter, thaw a frozen condensate pipe. Reset once — if F28 returns, call a Gas Safe engineer.
Why does F28 happen in cold weather?
Most often a frozen condensate pipe. The external pipe freezes and backs up, stopping the boiler firing. Thawing it and resetting usually clears it.
F28 keeps coming back after I reset — why?
The no-flame fault is still there. Repeatedly resetting won't fix a gas or ignition fault — it needs diagnosing by an engineer.
Is Glow-worm F28 the same as Vaillant F28?
Effectively yes — Glow-worm and Vaillant share the same code system, so F28 is an ignition failure on both.
Are you Gas Safe registered?
Yes — registration 587401, and we repair Glow-worm boilers across East London.
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