What the F29 code means
F29 is a flame failure that happens after the boiler has already lit. The burner was running, then the flame detection circuit stopped seeing a flame. The boiler will usually try to relight, and if that does not work it shuts the gas off and displays F.29.
Glow-worm's installation manual for the Energy range lists F29 simply as flame loss, and the Betacom and Ultimate documentation describes it as loss of flame during operation. The difference from F28 matters. With F28 the boiler never got going. With F29 it was working and something interrupted it, which often points to a supply, flue or condensate problem rather than a worn ignition part. The same code on Vaillant ecoTEC boilers is covered on our Vaillant F29 page.
Common causes of F29
A short break in the gas supply
Glow-worm lists a temporary stop in the gas supply as a likely cause. A prepayment meter running out partway through a heating cycle, a gas pressure dip when several appliances are used at once, or a problem with the supply to your street can all do it.
A blocked or frozen condensate pipe
If condensate cannot drain away, it builds up inside the boiler and can put the flame out. Installer sources name a frozen condensate pipe as a common reason Glow-worm boilers show F29 in winter.
Flue gases being drawn back in
The manual mentions flue gas recirculation, where exhaust gases are pulled back into the air intake. This can happen if the flue terminal is obstructed, if something has been built close to it, or in certain wind conditions. It is an engineer job to check. Glow-worm manuals set out minimum clearances around the flue terminal for this reason, so a new extension, fence or large shrub close to it is worth mentioning when you book.
Electrical and component faults
Poor earthing and a weak spark from the ignition transformer are also listed in the Energy manual. On some older models, such as the original Ultimate, the manual points to incorrect fan speed or gas circuit faults. An engineer will need to test these.
| Cause | What you might notice | Who fixes it |
|---|---|---|
| Prepayment credit ran out | Other gas appliances also stopped | You, by topping up |
| Frozen or blocked condensate pipe | Cold snap, gurgling sounds | You (frozen pipe), engineer (internal blockage) |
| Flue gas recirculation | F29 in windy weather or after building work nearby | Gas Safe engineer |
| Low gas pressure | F29 when the hob and boiler run together | Gas Safe engineer or your gas network |
| Ignition, earth or fan faults | Supply fine, F29 keeps returning | Gas Safe engineer |
Safe checks you can do yourself
- Check whether other gas appliances are working. If the hob will not light, the issue is the supply.
- Look at your gas meter. If it is a prepayment meter, check there is credit left.
- Make sure the gas isolation valve under the boiler is fully open, with the handle in line with the pipe.
- In freezing weather, check the condensate pipe where it leaves the house. If it is frozen, thaw it with warm (not boiling) water or a hot water bottle. Our frozen condensate pipe guide explains how.
- Look at the flue terminal outside, without touching it. Tell your engineer if anything is blocking it, such as a plant, a new fence or a stored item.
- Reset the boiler as your manual describes. Stop after two or three attempts if F29 keeps coming back.
Do not touch or try to clear anything from the flue yourself, and never remove the boiler casing. If you smell gas, turn off the supply at the meter if it is safe to do so and call the National Gas Emergency Service on 0800 111 999.
When to call a Gas Safe engineer
Call a Gas Safe registered engineer if F29 keeps happening after you have ruled out the gas supply and the condensate pipe. It is also worth booking one if the fault shows up mainly in windy weather, or if something has recently been built or planted near the flue. The engineer will check the gas pressure while the boiler is running, inspect the condensate trap, check the flue for recirculation and test the ignition and flame detection parts.
Tell them when the fault happens. F29 that only appears during long heating runs, or only when you are cooking on the hob at the same time, gives a useful clue.
Typical repair costs in the UK
If the cause is a prepayment meter or a frozen pipe, there is no cost. Otherwise these are typical ranges, which will vary by region.
| Job | Typical UK cost |
|---|---|
| Engineer call-out and diagnosis | Typically £80 to £150 |
| Cleaning the condensate trap | Typically £80 to £150 |
| Replacing the electrode | Typically £90 to £180 |
| Adjusting or altering the flue | Typically £150 to £400 |
| Replacing the gas valve or fan | Typically £200 to £400 |
How to stop F29 coming back
Keep your prepayment meter topped up, particularly during cold spells. Keep the area around the flue terminal clear and do not build or plant close to it without asking an engineer. If your condensate pipe freezes regularly, ask a Gas Safe registered engineer about insulating it or changing its route. An annual service includes cleaning the condensate trap and checking the burner and flue, which covers most of the common causes. Our boiler service cost guide has more detail.