An F28 fault on a Glow-worm boiler means it has tried to ignite and failed, so it has locked out for safety.

There are three checks worth doing before you call anyone.

What F28 actually means

The boiler attempts ignition and looks for a flame signal. Without one it stops rather than continuing to send gas to an unlit burner. Glow-worm and Vaillant share a parent company and use similar code conventions, which is why the code matches the Vaillant F28.

What you can safely check yourself

Check whether other gas appliances work. If the hob will not light, the supply is the problem, not the boiler.

Check prepayment meter credit if you have one.

Then reset. Two or three attempts maximum.

When to stop, and why

What causes it beyond the simple checks

A failed ignition electrode, a dirty flame sensor, a gas valve fault, low incoming gas pressure, a blocked flue, or a frozen condensate pipe in cold weather.

How Vantage can help

We are Gas Safe registered and cover Hertfordshire, Bedfordshire and Cambridgeshire, with an emergency line answered 24 hours a day.

Frequently asked questions

Is it the same as the Vaillant F28?

The convention is shared, and the checks are the same. The appliance is still different.

How many resets?

Two or three at most.

Could it be the weather?

A frozen condensate pipe is a common winter cause, often with a gurgling noise.

Related fault codes

Other Glow-worm codes: Glow-worm F22

The same problem on other makes (ignition and flame faults): Vaillant F28 · Vaillant F29 · Vaillant F27 · Ideal L2 · Ideal F2 · Baxi E133 · Viessmann F4

See also our guide to boiler not firing up, the full boiler advice section, and boiler repair.

When to call an engineer

If the fault keeps returning after a reset, it is telling you something is degrading rather than broken. Call 01462 506374 and we will diagnose it properly rather than swapping parts and hoping. Gas Safe registered 956889, 12 months on our own labour.