In This Guide
What Does the Vaillant F22 Error Code Mean?
F22 is Vaillant’s low water pressure fault code. It appears when the boiler detects that the pressure in the sealed heating system has dropped below the level it needs to circulate water safely, so it locks out rather than run dry and damage the pump or heat exchanger. In plain terms, there is not enough water in the system. You will usually see it on ecoTEC and similar Vaillant models, and it normally leaves you with no heating and no hot water until the pressure is restored. It is one of the most common Vaillant faults 0800 Homefix is called out to across London and the South East, and the good news is that a one-off F22 is often something you can fix yourself in a few minutes. The sections below explain what causes it, how to repressurise safely, and when a recurring F22 means something bigger.
What Causes a Vaillant F22 Fault?
F22 always comes back to the same thing, too little water pressure, but the reason the pressure dropped is what matters. A one-off drop after maintenance is harmless. A pressure that keeps falling points to a leak or a failed component. The common causes are set out below.
|
Cause |
What happens |
Typical fix |
|
Recently bled radiators or drained the system |
Releasing air or water drops the pressure below the safe threshold |
Top up through the filling loop to around 1.2 bar on a cold system |
|
A small leak in the system |
A slow leak from a radiator, valve, pipe or joint lets pressure fall over days |
Trace and repair the leak; a Gas Safe engineer locates hidden ones |
|
Gradual pressure loss over time |
Sealed systems lose a little pressure naturally through minor air ingress |
An occasional top-up; if it is frequent, have the cause checked |
|
Faulty pressure sensor |
The sensor misreads the pressure and triggers F22 when the pressure is actually fine |
A Gas Safe engineer tests and replaces the sensor |
|
A dripping pressure relief valve |
A PRV discharging water outside slowly bleeds pressure out of the system |
A Gas Safe engineer inspects and replaces the valve |
|
Failed expansion vessel |
A waterlogged vessel causes pressure to swing and can leave it low when cold |
A Gas Safe engineer recharges or replaces the vessel |
The useful test is what happens after you top the pressure up. If it holds steady, it was almost certainly a one-off from bleeding radiators or natural loss, and nothing more is needed. If it drops again within hours or days, water is escaping somewhere, and that is when it needs an engineer rather than another top-up. A persistent F22 is often linked to a dripping pressure relief valve, which is covered in full in our guide to a boiler pressure relief valve dripping.
How Do You Fix a Vaillant F22 Error?
Most one-off F22 faults are cleared by repressurising the system, which is a safe job for a homeowner. Work through it carefully.
First, find the filling loop. This is the braided silver hose underneath the boiler, connecting the heating system to the mains water supply, with a valve at each end. Both valves should normally be closed, meaning the handles sit across the pipe rather than in line with it.
Second, top up with the boiler cold. This matters. Water expands as it heats, so the pressure you set on a cold system rises once the heating comes on. If you fill to 1.5 bar cold, the pressure can climb past 2 bar when hot and start forcing water out of the pressure relief valve, which then causes the pressure to drop again later. Turn the boiler off, let it cool, then open both filling loop valves slowly and watch the gauge. Close them as soon as it reaches around 1.2 bar. That leaves room for the pressure to rise into the normal 1 to 1.5 bar range once the system warms up.
Third, reset and check. Turn the boiler back on and clear the F22 code with the reset button. If the boiler fires and the pressure holds over the next day or two, the fault is resolved. If the pressure drops again without you touching the filling loop, do not keep topping it up. That is a leak or a faulty component, and the next step is a diagnosis. You can arrange that through the 0800 Homefix boiler repair service.
When Should You Call a Gas Safe Engineer for an F22 Fault?
Call an engineer if the pressure will not hold after topping up, if F22 returns repeatedly, or if you can see water pooling near the boiler, radiators or pipework. A pressure that keeps falling means water is leaving the system somewhere, whether through a visible drip, a hidden leak under floors, a dripping relief valve or a failing expansion vessel. Tracing a hidden leak and any work on the sealed system, the pressure sensor, relief valve or expansion vessel needs a Gas Safe registered engineer, so a recurring F22 is the point to stop topping up and book one.
What Does an 0800 Homefix Engineer Do About an F22 Fault?
An 0800 Homefix engineer works out why the pressure is dropping rather than just refilling it. They check the pressure sensor is reading correctly, inspect the pressure relief valve and expansion vessel, and look for leaks across the radiators, valves, pipework and boiler components. Where the leak is hidden, they can trace it rather than guess. Once the cause is found they carry out the repair, whether that is replacing a faulty sensor, sorting a dripping relief valve, recharging or replacing the expansion vessel, or fixing a leaking joint. Every engineer is Gas Safe registered, and the team covers London and the South East seven days a week, 365 days a year, so an F22 that has left you without heating does not mean a long wait.
How Much Does It Cost to Fix a Vaillant F22 Fault?
0800 Homefix does not charge a call-out fee. The visit is charged as the first hour of labour, paid in advance, and any further repair work, whether that is a pressure sensor, a relief valve or tracing a leak, is quoted and agreed with you before it begins, so nothing is a surprise once the engineer is on site. The exact rate and what the first hour covers are set out in full on the rates page. For peace of mind after the repair, 0800 Homefix guarantees its labour for 12 months, and the manufacturer guarantees any replacement parts for 12 months.
How Do You Prevent the F22 Fault Coming Back?
A one-off F22 is nothing to worry about, but a recurring one is worth preventing. The single most effective step is an annual boiler service, which lets an engineer check the pressure sensor, the relief valve and the expansion vessel, and catch a slow leak before it leaves you without heating. You can book this through Vaillant boiler servicing. Beyond that, glance at the pressure gauge now and then, top up on a cold system rather than a hot one, and if you find yourself repressurising more than once or twice a year, treat that as a sign of a leak to be investigated rather than a chore to keep repeating.
Frequently Asked Questions
How do I fix an F22 error on my Vaillant boiler?
Repressurise the system using the filling loop. With the boiler cold, open both filling loop valves slowly until the gauge reads around 1.2 bar, then close them and reset the boiler. Filling on a cold system leaves room for the pressure to rise into the normal range once the heating warms up.
What pressure should a Vaillant boiler be?
Between 1 and 1.5 bar when the system is warm. Because pressure rises as the system heats, top up to around 1.2 bar on a cold boiler so it settles within that range in use. Filling to 1.5 bar cold can push the pressure too high once hot.
Why does my Vaillant boiler keep losing pressure and showing F22?
If the pressure drops again soon after topping up, water is escaping from the system. The usual culprits are a leak in a radiator, valve, pipe or joint, a dripping pressure relief valve, or a failed expansion vessel. Topping up will not fix any of those, so it needs a Gas Safe engineer to find and repair the cause.
Can I fix an F22 fault myself?
You can safely repressurise the system through the filling loop, which clears most one-off F22 faults. If the pressure will not hold, or the fault keeps returning, the cause is a leak or a faulty component, and that must be handled by a Gas Safe registered engineer. 0800 Homefix can diagnose and repair it.
Is F22 the same as F75 on a Vaillant boiler?
No. F22 is low water pressure, while F75 is a pump or pressure sensor fault where the boiler detects no pressure change when the pump starts. They can feel similar because both leave you without heating, but they have different causes. Our guide to the Vaillant F75 fault covers that one.
Is a Vaillant F22 fault an emergency?
It is not dangerous, but it usually leaves you with no heating or hot water, so it is worth resolving quickly. A single top-up often fixes it. If the pressure keeps dropping, book an engineer rather than repeatedly refilling, since that points to a leak that will only get worse.
Spotted an F22 on Your Vaillant Boiler?
If topping up the pressure has not held, book an 0800 Homefix Gas Safe registered engineer to find out why. We cover London and the South East seven days a week, 365 days a year, with no call-out fee and a 12-month labour guarantee. Book online or call the team to get your heating and hot water back on.
Helpful Resources
- Gas Safe Register, to check any engineer’s registration: https://www.gassaferegister.co.uk/
- Vaillant’s own boiler support and guarantee information: https://www.vaillant.co.uk/
Spotted Any of These Warning Signs?
Our leak detection specialists cover London and the South East using acoustic detection, thermal imaging and moisture meters — no unnecessary damage, full written report, available 7 days a week.
Editorial note: This article is intended as a general homeowner guide. All plumbing work on supply pipes should be carried out by a qualified, WaterSafe-registered plumber. If you suspect a gas leak, leave the property immediately and call the National Gas Emergency Service on 0800 111 999.
