Fault F22: Troubleshooting Your Vaillant Boiler
For Optimal Performance


If you’ve stumbled upon the F22 fault code on your Vaillant boiler, don’t hit the panic button just yet. We’ve got your back! While it might seem like a hiccup, dealing with the F22 error is a common occurrence, and with a bit of troubleshooting magic, you’ll have your boiler back in top shape in no time. In this blog, we cover what the F22 fault means, possible causes and remedial steps to ensuring warmth and comfort is quickly resorted in your home.

What Does An F22 Fault Code Symbolise On A Vaillant Boiler?

If you see the F22 code on your Vaillant boiler, think of it like a gentle tap on the shoulder from your boiler, saying, “Hey, I need a little attention”. It’s usually nothing serious – just a signal that the water pressure might be a little low. When there’s too little water pressure your boiler will not be able to fire up. Your boiler will ‘lockdown’ and there will be no hot water coming from your taps or shower.  You’ll also notice that your radiators won’t be warming up when the heating is on. With a little boiler TLC, you will soon have things running smoothly again.

In addition to the F22 code, you may also notice that a number (such as 0.2) flashes up on your boiler’s display screen. This number represents the pressure level inside the system and is measured in bar. The ideal water pressure for a Vaillant boiler is around 1 to 1.5 bar. If the number on display is below 1, you will need to increase the water pressure.

Boiler pressure levels can differ among various models, so it’s wise to consult your Vaillant boiler’s manual to pinpoint the ideal pressure level tailored specifically for your unit.

Why Does My Boiler Have Low Water Pressure?

A boiler can experience low water pressure due to several reasons including a water leak in the system, bleeding of radiators, or issues with the pressure relief valve. Additionally, the expansion vessel, which absorbs excess water during heating, may lose pressure over time. Identifying and addressing these issues promptly helps maintain the proper functioning of the boiler. Vaillant boiler F22 faults happen because air finds its way into the system, meaning you may have to top up the pressure a few times a year. The drop in pressure will be gradual. If you experience a very sudden loss of pressure or you are having to top up the boiler’s pressure level much more frequently, there is likely an underlying issue that needs to be dealt with.

How Would A Heating Engineer Fix A Failed Expansion Vessel?

Typically located just inside the boiler casing, an expansion vessel is the vital component in a boiler that keeps the pressure stable while water heats and cools and they are. During the heating process the vessel absorbs excess water and over time it can lose pressure. A Gas Safe Registered heating engineer will likely begin by turning off the boiler and draining the system. They will then locate the expansion vessel, check its pressure, and recharge it using a pump or compressor if necessary. They’ll address any leaks in the vessel or connections, close the valves, refill the system, bleed air from radiators, and restart the boiler. This process ensures the expansion vessel can efficiently absorb excess water during heating, maintaining optimal system pressure.

What Is Involved In Finding And Fixing A Leak In A Central Heating System?

If you’ve got a water leak causing low pressure, here’s how a qualified heating engineer would handle it:

  1. They’d take a good look around your boiler and pipes for any visible signs of water – think of it like searching for clues. Checking the pressure with a gauge is their next move; as we know, abnormal pressure can be a sign of a sneaky leak.
  2. To narrow down the search, they might isolate different sections of the heating system. Inspecting pipes for cracks, corrosion, or loose connections is crucial. They will also give the pressure relief valve and other boiler parts a once-over to ensure everything is working as it should.
  3. For a more specific diagnosis, professionals might use dye tests. These tests involve using special dyes that can trace the path of the water and reveal the location of the leak. Once the issue is identified, they’ll proceed with the necessary repairs, whether it’s fixing a faulty valve, addressing a pipe issue, or solving any other problems causing the leak such as a defective water pressure sensor.

How Can I Correct Pressure Issues In My Vaillant Boiler?

If you feel confident enough to do so, you can try to repressurise your boiler. However, we always recommend enlisting the help of professional heating engineer to carry out works on a boiler to ensure it is done correctly and without risk to your safety. To do this, you’ll need to turn the valves connected to each end of the boilers filling loop. This may remove the F22 code and restore your system to normal. It is important to note that you shouldn’t have to do this more frequently than once or twice a year.

Below: An exmaple of a filling loop underneath a combi Vaillant boiler. If you have a system or heat only boiler, your filling loop may be connected to the pipework or attached to an external expansion vessel.


Remember, if the F22 comes back soon after increasing the pressure, it is likely to be an underlying issue that needs to be addressed by a Gas Safe Registered engineer.


While you may feel confident topping up the boiler yourself, it’s really important not to tackle repairs on your own. DIY attempts might end up causing significant harm to your boiler and even pose a risk of carbon monoxide exposure. Gas Safe heating engineers are professionals in handling heating systems, always following HSE regulations. So, if something’s up with your boiler, leave it to the experts who know how to keep things safe and snug!

Sometimes of course, simple old age is to blame. Just like us humans, things start to fail as we get older! Luckily, a boiler can be replaced!

How Can I Avoid Getting A Vaillant Boiler F22 Fault Code?

Prevention is always better than cure! If you want to prevent any boiler issues from occurring and therefore, being without heat or hot water for any length of time, the best thing you can do is keep up to date with servicing your gas boiler. A yearly boiler service is expected by home insurance providers and without it you could lose your manufacturer’s guarantee.

Many customers have their boiler serviced in late summer in preparation for winter. However, any time of year is suitable for a boiler service.

The Happy Dog Plumbing team are experts at unravelling any issue your Vaillant boiler throws our way – be it low water pressure, a loose connection, or a cranky broken part. Plus, we’re proud members of the Vaillant Advance approved installer scheme, meaning you can count on us for that extra-special advice, installation, and maintenance tailored just for Vaillant systems. No matter the mysterious fault code, we’ll fix things as soon as possible, ensuring your home stays cosy and energy-efficient throughout the year.