What causes the Vaillant F22 Fault Code
In the user manual, Vaillant defines the F22 as:
| Code | Meaning | Cause |
|---|---|---|
| F22 | Safety switch-off: low water pressure | No pressure or water pressure too low in the boiler, water pressure sensor defective, cable to pump or water pressure sensor loose/not connected/defective |
The Vaillant F22 fault code will appear when your boiler's water pressure drops below a safe level (below 0.5 bar). Without sufficient pressure your Vaillant boiler will not ignite, causing the boiler to lock out (i.e. stop working); it's a safety feature designed to stop the boiler from firing with little or no water and prevent damaging the heat exchanger.
The Vaillant F22 fault code isn’t as serious as some of the other fault codes we have covered, for example the F28. It is not usually associated with gas supply faults or broken boiler parts, so you can sometimes resolve the problem causing the Vaillant F22 Fault code yourself.
Although the problem is not necessarily dangerous, it is kind of urgent, as you will want to have heat back in your radiators and showers as soon as possible. Therefore, contact a Gas Safe engineer first, and while you wait you can follow some steps that can help you save the engineer's time and labour charges.
Steps to fix the Vaillant F22 Fault Code
1. Check the Water Pressure Gauge
The first thing to do once you see the Vaillant F22 Fault code, is to check your boiler’s pressure. Depending on the model of your Vaillant boiler, you will either find a physical pressure gauge on the front of the boiler or the digital version of it on the display panel. For normal boiler operation, the bar should be around the 1.5 mark and no lower than 1.0 mark.
Naturally, boilers always lose pressure with time, but this progression is very gradual. Once or twice a year, the pressure in the system will need to be topped up. If you are having to repressurise your heating system more often than that, it’s time to contact an engineer.
If the reading is within the range specified above, yet the boiler keeps switching off, there may be an underlying issue with the pressure sensor. If it is faulty, it can send signals to the PCB, your boiler’s control centre, that the pressure is lower than it actually is, forcing the boiler to lockout. In this case, you can replace the water pressure sensor, which will cost you anywhere between £12 and £40.
If, however, the reading is below the 1.0 mark, there is clearly a leak in the system. In some cases, this will be visible and in others, they might be tiny and occurring inside the system.
2. Inspect the heating system for leaks
Once you’ve determined that the pressure is lower than it should be, it is time to check for leaks. This is a crucial step since leaks can cause damage to the boiler's internal components, as well as plasterboards and flooring. If you have noticed a sudden pressure drop, there is a good chance you’ll find a larger, quite visible leak. Check the areas around radiators and the boiler itself, look for damp patches and check whether the pipework is wet.
If the system looks OK, chances are that there are leaks in the pump, the diverter valve or other internal components and it’s a good idea to call a Gas Safe engineer. They will be able to thoroughly inspect the system and seal any leaks with sturdy material, ensuring your boiler continues to operate safely and won’t get the Vaillant F22 fault code in the future.
Although there are products on the internet, such as LeakSeal, that claim to be suitable for you to use and seal any gaps yourself, it’s best to avoid using them. The material used in such products is almost identical to ordinary glue and will not provide a durable solution. In most cases, you should leave the repair to the experts.
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3. Top up your boiler pressure
Topping up your boiler pressure may sound complicated, but with modern boilers, it really isn’t. To do this, you will need to turn off the boiler, wait until it cools down and find the charging link, also known as the filling loop.
If you have the Vaillant EcoTec boiler, you will find two grey knobs with ‘closed’ written on them underneath your boiler. Simply turn these knobs to allow water in the system.
On other Vaillant boilers, the filling loop looks like a small flexible hose that connects two pipes together. You will usually find it below the boiler or sometimes in the cylinder cupboard. Both valves need to be opened to allow water into the system. Once you reach the optimum pressure, for Vaillant boilers that's around 1.3, close the valve.
For more instructions on how to change your Vaillant boiler pressure, click below.
How to increase boiler pressure
4. Reset your boiler
It's time to reset your boiler now that the sensor has been checked, leaks have been sealed, and the boiler's pressure has been restored. This should only be attempted after you've identified the leaks and sealed them with durable material.
To reset the boiler and clear the Vaillant F22 fault code, hold the reset button for five seconds. As the boiler resets, the PCB will check the readings from the water pressure switch, and, assuming it’s been topped up to the correct pressure, your boiler will fire up.
