Boilers · Fault code
Vaillant (and Glow-worm) F28 and F29 fault codes
On Vaillant boilers — and many Glow-worm models, which share parts — F28 means the boiler failed to light at start-up, and F29 means the flame was lost while it was running. Both usually point to the gas supply, a frozen condensate pipe, or the ignition and flame-sensing parts.
F29 that comes and goes is often a sign of low gas pressure or a flue issue, both of which need a Registered Gas Installer with a manometer and a flue gas analyser — not a guess.
What changes the answer
- F28 (will not light) or F29 (lights then goes out)
- whether other gas appliances work
- cold weather and an outdoor condensate pipe
- whether the gas meter has been changed or worked on recently
What you can check yourself
- check the hob or another gas appliance
- check the condensate pipe outside in freezing weather
- reset once using the reset button, following the manual
What to do next
If it locks out again after one reset, book a repair. Never take the casing off a gas boiler. Anything inside the case is a job for a Registered Gas Installer.
This page gives general information only. Christy needs to see your system — in person or from your photos — before he can give you firm advice or a price.