How to fix F22 Fault on a Vaillant Boiler

Have you been greeted with an F22 fault code on your Vaillant boiler? Are you without central heating and hot water? Fear not. In this article, we will explain what the fault code means, its possible causes and what you can do to fix it.

Vaillant boiler F22 fault code featured image

What does an F22 fault code mean on a Vaillant boiler?

There are three possible causes for an F22 error code on a Vaillant boiler. They are as follows:

  1. Low water pressure
  2. No water, or a lack of water inside the boiler
  3. A defective water pressure sensor

These issues will cause an F.22 fault code, and your boiler will turn off as a safety precaution.

How to fix an F.22 fault code

If it’s been a long time since your last boiler service, you may be experiencing a loss of pressure due to a lack of water in the system. In this case, you may be able to perform a quick fix yourself.

The ideal water pressure for a Vaillant boiler is around 1 to 1.5 bar. First, check your water pressure gauge. If it is fallen below 1, you will need to increase the water pressure.

How to Increase the Water Pressure

You can increase water pressure by topping up your central heating system. To top up your central heating system, follow these steps:

You may need a flathead screwdriver.

  1. Turn off the boiler. Your central heating system needs to be cool before beginning any of the next steps.
  2. Next, you will need to identify the filling loop. The filling loop is a silver connection between the mains and the central heating unit. (The filling loop looks like a silver tube. Take a look at the image below for reference). 
  3. Using the flathead screwdriver, open the isolation valve by turning it 90 degrees anti-clockwise until the valve head is in line with the pipe.
  4. Press one of the buttons on your boiler display to clearly see the water pressure display.
  5. Slowly open the second isolation valve while monitoring the boiler display. This will allow water into the central heating system.
  6. Close the second isolation valve when the water pressure reaches 1 and 1.5 bar.
  7. Close the first isolation valve and check that both valves are completely closed.
  8. Turn on the boiler. The system may go through a short start-up process. 
  9. Allow 20 to 30 minutes for your radiators to heat up.
  10. Check your radiators from top to bottom to ensure they are running correctly.
  11. Finally, check the boiler display to ensure the water pressure is between 1 and 1.5 bar.

If the f.22 fault code has gone and your boiler is operating correctly, you have successfully repaired your boiler!

Vaillant filling loop

Image: A filling loop with two isolation valves on each end.

I repressurised my boiler, and the F.22 code is still there

If your water pressure is still low after repressurising your boiler or becomes low a few days later, you may have a leak in your central heating system

How to find a leak in your central heating system

The first place to look for a water leak in your central heating system is around the boiler. Check for any drips or residue around your boiler while looking for water damage. An obvious sign of a leak is puddles of water under pipework and the boiler itself.

The problem with water leaks is it only takes a minimal leak to cause a loss of water pressure. Continuous leaks will cause your boiler to overwork, costing you more money on energy bills and decreasing the longevity of your boiler.

Your best solution is to call a central heating leak detection expert. A leak detection expert uses precise tools, including thermal imaging, to detect leaks at their source. As a result, you can save time looking around your entire home for a leak and prevent the possibility of water damage to your home.

Defective water pressure sensor

Defective water pressure sensors are pretty rare on a Vaillant boiler; however, they can happen over time if the boiler isn’t well maintained. Limescale and carbon build-up can prevent the sensor from signalling water pressure changes.

A water pressure sensor is a device that is designed to measure the pressure of water in a plumbing system and transmit this information to a controller or other device. If the water pressure sensor is defective, it may not accurately measure the water pressure, which can lead to problems with the system, such as incorrect water flow or inadequate water pressure.

Defective water pressure sensors can also cause problems with other parts of the plumbing system, such as valves, pumps, and control systems. In order to fix a defective water pressure sensor, it may be necessary to replace the sensor or repair it if possible to do so. It is important to address a faulty water pressure sensor as soon as possible, as it can lead to more severe problems if left unchecked.

How to check the water pressure sensor

Listen to your boiler; if you can hear the boiler pump working but no hot water or heating, your pressure sensor is likely defective.

If your pressure sensor is defective, call a Gas Safe registered engineer who will need to clear the debris and potentially replace the sensor.

Prevention is cheaper than cure!

The best way to prevent boiler breakdowns is by arranging an annual boiler service. Many customers opt to have their boiler serviced in autumn in preparation for winter. However, any time of year is suitable for a yearly service.

An annual service will address issues before they become serious problems. As a result, you save money on boiler repairs, replacement parts, and even replacing your boiler!

About the author

PHS Trades Team are experts in Heating, Plumbing and Gas Services. We provide expert Boiler Repair and Boiler Servicing to homes and businesses across the Southeast.

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