What does the Vaillant F28 error code mean?
F28 is one of the most common Vaillant faults: the boiler has tried to light, failed, and locked out. It's almost always a gas supply, ignition or flame-detection issue. You can quickly check whether other gas appliances work before calling an engineer.
What causes the Vaillant F28 fault?
The F28 error on a Vaillant boiler is most commonly triggered by:
- No or low gas supply (check other gas appliances, meter and prepayment meter credit)
- A faulty ignition electrode or its lead
- A blocked or frozen flue/condensate in cold weather
- A failing gas valve or electronic control board
How to fix the Vaillant F28 boiler fault
Follow these steps. If the code returns after you have completed them, stop and call a Gas Safe engineer.
- 1.Check that other gas appliances (hob, fire) still work — if they don't, the issue is the gas supply, not the boiler, and you should call your gas supplier or National Gas Emergency on 0800 111 999.
- 2.If only the boiler is affected, reset it once; if F28 returns, do not keep retrying.
- 3.Book a Gas Safe engineer to test ignition, gas valve and flue.
Frequently asked questions about the Vaillant F28
What does F28 mean on a Vaillant boiler?
F28 means the boiler attempted to ignite and failed, then locked out. It's usually a gas-supply, ignition electrode or flame-detection fault.
Can I fix a Vaillant F28 myself?
Check your gas supply is working by testing another appliance and checking your prepayment meter has credit. Beyond that, F28 needs a Gas Safe engineer — it's a gas-related fault.
Is F28 the same as F29?
No. F28 means the boiler couldn't ignite at all at start-up; F29 means a flame was established during operation and then went out. The causes overlap but the timing differs.