Quick answer: The Vaillant F22 fault means low water pressure — the boiler has detected too little water in the system (a dry-fire condition) and shut down to protect itself. It’s often fixable at home by topping up the pressure via the filling loop, but a persistent F22 usually points to a leak that needs an engineer.
An F22 on your Vaillant display is one of the more common faults we get called about, and the good news is it’s frequently something you can sort yourself. Here’s what it means and how to fix it. First, a quick note: if your Vaillant is over about seven years old and F22 keeps returning, ageing systems that repeatedly lose pressure can cost more in call-outs than they’re worth, so it’s worth considering a new boiler installation rather than chasing recurring faults.
What Does the Vaillant F22 Error Code Mean?
F22 indicates low water pressure — there isn’t enough water circulating, so the boiler shuts down to avoid running dry and damaging itself.
Your heating system needs to hold a certain pressure to work safely. When it drops too low, the F22 fault stops the boiler firing. It’s a protective cut-out, not a breakdown in itself.
What Causes a Vaillant F22 Low Pressure Fault?
The main causes are a gradual pressure drop over time, a leak somewhere in the system, or recently bled radiators.
- Natural pressure loss — systems slowly lose a little pressure over months
- A leak — in pipework, radiators, or a boiler component
- Recently bled radiators — releasing air drops the pressure
- A faulty pressure sensor — less common, but possible
How Do You Fix a Vaillant F22 Error?
Top up the system pressure using the filling loop until the gauge reads around 1–1.5 bar, then reset the boiler.
- Find the filling loop — usually a silver braided hose beneath the boiler
- Open both valves slowly to let water in, watching the pressure gauge
- Aim for 1–1.5 bar (cold), then close the valves
- Reset the boiler and it should fire back up
If the pressure won’t hold and F22 returns within days, you likely have a leak — that’s the point to book a boiler repair rather than keep re-pressurising.
Why Does My Vaillant Keep Showing F22?
A recurring F22 almost always means a leak somewhere in the system — repeatedly topping up masks the problem rather than solving it.
If you’re refilling every few days, water is escaping somewhere. Sometimes it’s visible at a radiator valve or pipe joint; often it’s hidden. Keeping the pressure topped up indefinitely isn’t a fix and can cause other issues, so it’s worth getting the leak traced.
Can Servicing Prevent Vaillant F22 Faults?
Yes — an annual service checks pressure, seals and the expansion vessel, catching the slow leaks and component wear that lead to F22 before they leave you cold.
Regular maintenance is the quiet hero here. A yearly boiler service picks up on failing seals and pressure problems early, and in Scotland an autumn service means you head into winter with the system holding pressure properly.
When Should You Call an Engineer for Vaillant F22?
Call an engineer if the pressure won’t hold, if you can’t find the filling loop, or if F22 keeps returning despite topping up — all signs of a leak or sensor fault.
Topping up once or twice is fine to do yourself. Beyond that, you need someone to find why the water’s disappearing.
Local Vaillant Boiler Repairs Across Edinburgh and Scotland
We’re based in Edinburgh and cover central Scotland, so we can get to a stubborn F22 quickly and trace any leak properly. If your Vaillant keeps dropping pressure, get in touch with our Gas Safe engineers and we’ll sort it at source.
Frequently Asked Questions About the Vaillant F22 Error
What’s the difference between the Vaillant F22 and F75 codes?
F22 is a straightforward low water pressure fault, while the Vaillant F75 error relates to the pump or pressure sensor not detecting a pressure change. F22 is often a DIY top-up; F75 usually needs an engineer.
What pressure should my Vaillant boiler be at?
Aim for around 1–1.5 bar when cold. Below 1 bar and you’re likely to trigger F22; topping up to the middle of that range gives you a bit of headroom.
My Vaillant shows F28 instead of F22 — is it the same fix?
No. The Vaillant F28 error is an ignition failure, not a pressure fault, so re-pressurising won’t help. F28 calls for checking your gas supply and condensate pipe instead.
Can I keep using my boiler with a low F22 pressure warning?
It’s best not to. The boiler locks out precisely to avoid running with too little water, which can cause damage. Top the pressure up first, and if it won’t hold, get the leak found.
