Vaillant F22 Fault Code: What It Means and What to Do

If your Vaillant boiler has flashed up F22 and gone cold, you're probably standing in a chilly kitchen wondering whether this is a five-minute fix or an engineer callout. The good news is that F22 is one of the more common Vaillant fault codes, and in many cases it points to something you can check yourself before booking anyone out.

What does F22 mean on a Vaillant boiler?

F22 indicates low water pressure in the system, or a fault with the pressure sensor itself. Vaillant boilers, like most modern combis, need a minimum system pressure (usually around 1 bar) to fire safely. If pressure drops too low, the boiler locks out to protect itself and the flame won't light. You'll typically see F22 alongside a pressure gauge reading below 1 bar, or occasionally sitting at zero even when there's water in the system, which usually points to the sensor rather than an actual leak.

Common causes of F22

A few things tend to cause this fault:

• A recent radiator bleed that wasn't followed by repressurising
• A slow leak somewhere in the pipework or at a radiator valve
• A faulty pressure relief valve letting water escape
• A failed pressure sensor giving a false low reading
• Air in the system after work was carried out nearby

If pressure keeps dropping repeatedly over days or weeks rather than staying steady once topped up, that's a sign of an underlying leak rather than a one-off blip. Our pressure guide covers this in more detail, including where leaks commonly show up.

How to fix F22 yourself

Most Vaillant boilers have a filling loop, a flexible braided hose connected under the boiler. To repressurise:

1. Turn off the boiler.
2. Locate the filling loop and open both valves slowly until the gauge reads between 1 and 1.5 bar.
3. Close both valves firmly.
4. Turn the boiler back on and reset it if needed.

If the pressure holds steady over the next hour, you've likely just topped it up after a bleed or minor air release. If it drops again quickly, don't keep repeating the process, that usually means a leak needs finding and fixing rather than masking.

If you've recently bled a radiator, it's worth reading our guide to bleeding radiators properly, since trapped air is a frequent trigger for F22 straight afterwards.

When to call a Gas Safe engineer

Call a professional if:

• Pressure drops again within a day or two of topping up
• You can see damp patches, staining or drips near the boiler or radiators
• The fault code stays on screen even after repressurising correctly
• You're not confident locating or using the filling loop

Any gas appliance work in the UK should only be carried out by a Gas Safe registered engineer, and you can check an engineer's registration on the Gas Safe Register site before letting anyone near your boiler. Vaillant also publishes fault code guidance on the Vaillant support pages if you want to cross-check the code your specific model is showing.

Could F22 mean your boiler needs replacing?

Occasional F22 faults on an otherwise reliable boiler are usually nothing serious. But if your boiler is older, needs frequent repressurising, or is showing other issues alongside it, it might be worth reading our piece on signs you need a new boiler. Regular servicing also catches slow pressure loss and sensor faults before they cause a full lockout, and the Energy Saving Trust has good general advice on keeping heating systems running efficiently.

If repeated faults are becoming a pattern rather than a one-off, it may be time to weigh up a repair against a replacement. Norvera offers fixed prices with Gas Safe registered engineers across the Midlands, so if you'd rather have someone take a proper look, you can get a fixed price or, if it's urgent, book emergency help.