Vaillant boiler F28 fault code

How to Fix Vaillant Boiler F28 Fault: Repair Guide

Last updated on October 28th, 2023

The Vaillant boiler F28 fault code, and all Vaillant boiler fault codes, show on the display when there is a problem and your boiler locks out.

Vaillant uses them to show you what might be wrong with the boiler not firing up.

I have been a full-time boiler repairer for over a decade and having fault codes on the screen when I arrive is very welcome.

In this post, I’ll go through some of the reasons for your F28 fault and some potential fixes.

Vaillant combi boiler display

What Does F28 Mean on a Vaillant Boiler?

Having fault codes on the screen is a great way to help diagnose your boiler problems.

Here is what the Vaillant Ecotec manual (PDF) says about their F.28 fault:

What Does F28 Mean on a Vaillant Boiler
F.28 Vaillant boiler meaning

The most likely cause of an F28 fault is the boiler has been locked out due to a gas supply fault.

It could also mean that a part on the boiler is broken and needs to be replaced, but most of the time in my experience it is a gas issue.

Having no gas can be checked quite easily without having to open up the boiler.

How to Fix F28 Fault on a Vaillant Boiler

To fix the F28 fault code the first thing I would do is check the following:

  1. The gas is turned on at the gas meter.
  2. If you have a prepayment gas meter, then make sure you are in credit, as this is quite a common situation I come across.
  3. If you have other gas appliances, like a gas hob or gas fire, then check to see if these are working to find out if you have a gas supply problem. If they don’t work, then you might have to contact your gas supplier.
Gas meter turned off
Gas meter turned off

Other Causes of an F28 Fault Code

A gas supply problem is the most common cause of an F28 error code, but here are some other potential causes:

  • Faulty gas valve: The gas valve controls the gas to the boiler and might need to be replaced
  • Worn-out spark electrodes: The spark electrodes light the burner and might need to be replaced
  • Faulty PCB (printed circuit board): The PCB is the brain of the boiler and might need to be replaced
  • Frozen condensate pipe: If it’s freezing outside, then having a frozen condensate pipe is possible. You can pour hot water on it to melt the frozen condensate and then reset the boiler.

Vaillant F28 Fault Boiler Reset

The first thing I would do on a boiler that is not working, no matter what fault code is showing, is to check the pressure and reset the boiler.

Knowing how to reset a Vaillant boiler is the simplest way to get your boiler working again, as it might have just locked out.

To reset a Vaillant boiler, you must find the reset button. This is usually a flame with a line through it.

Vaillant boiler reset button
Vaillant reset button

You have to press the button to reset the boiler. Sometimes you have to hold it down for 3 seconds, but on some Vaillant boilers, it just needs to be pressed.

If your Vaillant F28 won’t reset then you have a problem that needs to be fixed before it will reset.

Vaillant Boiler Guides


A Vaillant F28 error on your boiler can sometimes be easily fixed without opening the boiler.

Make sure to verify you are getting gas by checking the gas meter ECV and that you have credit if you use a pre-payment gas meter.

If it's snowing or sub-zero temperatures outside, then you will most likely have to thaw the condensate pipe outside after it freezing.

Any boiler part replacements and testing should be done by a Gas Safe registered engineer.

Feel free to ask me any questions in the comment section below and I’ll try my best to help.

Please share this post if you find it helpful.


How do you clear the fault code on a Vaillant boiler?

To clear the fault code on a Vaillant boiler, you must reset the boiler.

If the fault code appears after resetting the boiler, you must find and repair the problem causing it to lock out and show a fault code.

Why is my Vaillant boiler not turning on?

If your Vaillant boiler is not turning on at all (nothing on the display), then you probably have an electric supply issue.

You should check the fused spur switch that should be next to the boiler. Make sure it is switched on and the 3 amp fuse is good.

It could also be that the fuse at the main board (consumer unit) has tripped, so you should check there too.

What do I do if I have no gas supply?

If you have no gas after making sure it’s turned on at the gas meter, you need to call your gas supplier (eg British Gas).

There could be a problem with your account or a gas supply issue to your house that they are not aware of.

Any gas supply issues from the street up to the gas meter are the gas suppliers’ responsibility and won’t cost you a penny to fix.

What does F29 mean on a Vaillant boiler?

The Vaillant F29 fault is similar to the F28 fault and can be caused by the same problems.


  • Steven Reid

    I am a full-time plumber and Gas Safe registered engineer. I incorporated Housewarm Ltd. in 2011 to provide heating and plumbing services to homes in Newcastle upon Tyne, England. I now blog about what I've learned over the years to help DIYers and plumbers.

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