Vaillant Boiler F29 Fault – Error Code Guide

The Vaillant F29 error code is triggered by flame failure and affects the EcoTec models of Vaillant boilers. 

This error code is likely to be triggered by faulty parts, insufficient gas supply or blockages in the flue pipe, so it should be left to a Gas Safe Engineer to resolve – you should not attempt to resolve this issue yourself.

What Does a Vaillant F29 Error Mean?

This error means that the flame has stopped working during operation, which triggers a boiler lockout. The flame is necessary for the boiler to function and heat the water, so until this error is resolved you will be left without heating and hot water.

The boiler will lockout as a result of this error code because it is related to the flame operation and could involve a problem with the gas supply, and it could be unsafe for people inside the property if the boiler were to keep operating, or possible damage the internal components of the boiler.

What Causes a Vaillant F29 Error?

There are a few possible causes of the F29 error, which your engineer will be able to diagnose.

Gas pressure

The F29 can be triggered by the gas pressure being too low. The right level of gas pressure is integral for the boiler to function and for the flame to keep burning, so when the pressure is too low this causes flame failure. 

Low gas pressure is usually caused by a faulty or wrongly adjusted gas valve, although it is possible that it is caused by a gas leak or a blockage in the gas pipe as these pipes are small in diameter.

Flue Problem 

The flue is designed to expel dangerous gases produced from burning the gas to produce the flame, and when it is blocked it results in suboptimal pressure and internal temperature, causing the boiler to lockout and experience flame failure. When it is incorrectly installed this can also be a problem because a strong wind can cause the flame to go out.


This error code can display as a result of build-up in the burner. Over time, debris collects in the burner, which can make it difficult for the flame to ignite. This possibility is more likely if your boiler has not been serviced in a long time, as the burner will be cleaned at every service.

Ignition error

The ignition leads or electrodes are the components that create the spark which lights the flame within your boiler. If these are faulty or broken, this would prevent the flame from igniting and trigger the F29 error code.

All of the above causes lead to flame failure, and this is what prompts the boiler to lockout and the F29 error code to display.

Blocked condensate pipe

Another possible cause is that the condensate pipe, which expels waste liquid, has become blocked or frozen. This causes an increase in pressure in the boiler, leading to a lockout and flame failure. You can usually identify when this is the problem because you will also be able to hear a gurgling sound coming from the heating system.

How to Fix a Vaillant F29 Error

This boiler error should be fixed by a Gas Safe Engineer, who will be able to diagnose the problem and fix or replace any faulty parts.

If the issue has been caused by insufficient gas supply, an engineer will check whether the gas valve has been adjusted correctly, and re-adust it if not. If this doesn’t work, then they will replace the part for you.

If debris in the burner is the problem then an engineer will clean the burner, after which it should work – however, it is possible that the burner has been damaged by the debris and will need replacing. 

If an incorrectly installed flue pipe is the root cause then this can be reinstalled, or any blockages can be removed – and future blockages prevented by installing a flue guard.

Finally, if the error is down to the ignition leads or electrodes then these will likely need to be replaced.

Can you Fix a Vaillant F29 Error Yourself?

The F29 error code is caused by a flame failure, and the cause of this is most likely to do with electrical components or gas issues. 

This means that it can be very dangerous to attempt to deal with this error code on your own, and a Gas Safe Engineer should be called to diagnose and resolve the problem for you.

One possible cause you can safely deal with yourself is a frozen condensate pipe; once you have located the pipe and where the blockage or ice is (likely at the joint), you can simply pour hot water over it to relieve the blockage.

It is a good idea to turn off the gas supply to your property until the error has been resolved, however, in case the cause of the problem lies with the gas supply.

Can a Leak Cause the F29 Error?

Sometimes a boiler leak can cause damage to the electrical parts of the boiler, such as the ignition leads or electrodes – so if this is diagnosed as the cause of the fault then it’s possible that an internal leak is the source of the problem.

However, you should not try to diagnose this yourself – it should be left to a Gas Safe Engineer.

How Much Does It Cost to Replace a Boiler Burner?

The price varies from boiler to boiler, but you can expect to pay up to £400 for a new burner. Can I prevent the F29 error from happening?

The best thing you can do to prevent this error from happening is to have your boiler regularly serviced.

This will ensure your boiler is in tip-top shape generally, and also prevent specific issues like debris building up in the burner, incorrectly adjusted valves, and will catch faulty parts before they fail.

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