Quick answer: F22 means your Vaillant boiler's water pressure is too low. Top it up to between 1 and 1.5 bar using the filling loop, then restart the boiler. If F22 keeps coming back, water is escaping somewhere and you need an engineer.
What F22 means
Vaillant describes F22 as there being no water, or not enough water, in the boiler: in other words, the water pressure is too low. The boiler shuts down to protect itself until the pressure is restored.
Vaillant recommends contacting a qualified installer for faults. Topping up the pressure with the filling loop is a routine job most user manuals explain, but if you're unsure, leave it to an engineer.
How to fix it
- Check the gauge. When the heating is off and the system is cold, most boilers should read between 1 and 1.5 bar. If F22 is showing, it will be lower.
- Top up the pressure using the filling loop, as your user manual describes. Our step-by-step guide shows how: how to top up boiler pressure.
- Restart the boiler using its reset or restart button. F22 should clear once the pressure is back in range.
If you're not confident using the filling loop, or the gauge doesn't move when you open it, don't force anything. Call a Gas Safe registered engineer.
If F22 keeps coming back
Pressure that keeps dropping means water is escaping somewhere. Look for drips or damp around radiator valves, exposed pipes and under the boiler, and check whether the small copper pipe that runs outside from the boiler is dripping. If you can't find a leak and the code returns within days, book a Gas Safe registered engineer. Common causes include a hidden leak, the pressure relief valve or the expansion vessel.
Have boiler cover?
Call your provider before paying an engineer yourself. A repair like this is exactly what cover is for.
No cover yet? A new plan won't pay for a fault you already have, because problems that exist when you join aren't covered and there's a waiting period at the start. It can protect you next time.
Compare boiler coverRelated help
Last updated 30 October 2026