A Vaillant boiler showing F22 (or F.22) is telling you there is not enough water in the heating system. Vaillant calls this a dry fire fault. The boiler shuts down to stop itself overheating with too little water inside.
What causes F22?
- Low system pressure, the most common cause by far
- A leak somewhere on the heating system, such as a radiator valve or pipe joint
- Water released through the pressure relief valve
- Recently bled radiators, which lets water out as well as air
- A faulty pump, or a faulty pressure sensor giving a false reading
How to top up the pressure
Most combi boilers have a filling loop underneath, either a silver braided hose or a built-in key or lever. Your boiler manual shows exactly where it is.
- Turn the boiler off and let it cool.
- Find the pressure gauge on the front of the boiler.
- Open the filling loop valves slowly. You will hear water flowing.
- Watch the gauge and close the valves when it reads between 1 and 1.5 bar when cold.
- Turn the boiler back on and press reset if needed.
If you are not confident doing this, give us a call and we can talk you through it.
If F22 keeps coming back
Topping up once after bleeding radiators is normal. Having to top up every few days or weeks is not. It means water is escaping somewhere, or a part such as the expansion vessel or pressure relief valve has failed. Check under radiators and around visible pipework for drips, and look at the outside pipe from the pressure relief valve for any sign of water.
A Gas Safe engineer can test the expansion vessel, the pressure relief valve and the system for leaks, and find the real cause so you are not topping up all winter.
Phoenix Plumbing & Heating is a Gas Safe registered team based in Maidstone, covering Kent with 24/7 emergency cover. Call 01622 585169 or book online and one of our engineers will find the fault and give you a clear price before any work starts.