The Vaillant boiler F22 fault code (shown as F.22 on some displays) means the boiler has too little water in the heating system, or the water pressure is too low, so it has locked out to protect itself. You’ll usually have no heating or hot water until it’s fixed. The most common cause is lost pressure from a leak, recent radiator bleeding or a failing part. If your manual allows it, you can top the pressure up through the filling loop. If F22 comes back, the cause is a leak or a fault and you need a Gas Safe registered engineer.
| Question | Answer |
|---|---|
| What does F22 mean? | No or insufficient water in the system, or pressure too low |
| Normal cold pressure | About 1 to 1.5 bar. Check your manual for your model |
| Can I fix it myself? | Often, by topping up pressure through the filling loop, if your manual allows it |
| Call an engineer if | Pressure keeps dropping, you find a leak, or F22 returns after topping up |
What Does F22 Mean on a Vaillant Boiler?
The pressure here is the pressure in your sealed heating circuit, not the mains water pressure at your taps. Vaillant describes F22 as no or insufficient water in the product, or a water pressure that is too low. The boiler monitors pressure all the time. If it drops too far, the boiler stops firing so the heat exchanger and pump aren’t damaged. On most boilers the pressure gauge or display will show a reading well under 1 bar, often around 0.5 bar or lower, although the exact trigger varies by model.
Don’t confuse F22 with the Vaillant F23 fault code, which points to poor circulation, or with F75, which is linked to the pump or pressure sensor. If your pressure is actually too high rather than too low, see our guide to boiler pressure too high.
Common Causes of the Vaillant F22 Fault Code
| Cause | What It Can Look Like | Who Deals With It |
|---|---|---|
| Recent radiator bleeding | F22 appears soon after bleeding, because releasing air lowers the pressure | You can top up through the filling loop |
| A slow leak in the system | Pressure drops again within days or weeks. Damp patches, stains or drips | Engineer to find and repair |
| Leaking pressure relief valve (PRV) | Water dripping from the external discharge pipe | Engineer |
| Failing expansion vessel | Pressure shoots up when the system heats, the PRV opens and lets water out, then pressure is low once it cools | Engineer |
| Faulty pressure sensor, wiring or pump | The gauge looks normal but F22 shows, or the pump isn’t running | Engineer |
| Faulty filling device or solenoid valve, or a leaking loop connection | The boiler can’t refill properly, or water weeps from the loop hose or valves | Engineer |
Lost Pressure After Bleeding or a Small Leak
Bleeding radiators lets air and a little water out, so pressure falls afterwards. That’s normal and easy to put right. Tiny losses at valves and seals over many months are also normal, which is why an occasional top-up once or twice a year isn’t a worry. A leak is different. Water escapes from a radiator valve, a joint, a corroded pipe or the PRV, and the pressure keeps falling however often you top it up.
Expansion Vessel and Pressure Relief Valve
The expansion vessel absorbs the extra volume of water as it heats. If it loses its charge, pressure can climb too high when the system warms up, the PRV opens and discharges water outside, and the pressure is too low once it cools. That’s why a failing vessel can end in F22 even though the first symptom is high pressure. The PRV discharges through a separate external pipe, not the plastic condensate pipe. Both parts are sealed-system components, so they are engineer jobs.
Sensor, Pump and Filling Device Faults
A filling loop that is stuck open usually raises pressure rather than lowering it, but a leak at its connections can lose water. Vaillant also lists a faulty pressure sensor or its wiring, a loose or defective pump cable, an interrupted pump and a defective filling device valve as possible causes. These are less common than a simple loss of pressure, but they are why F22 can appear with a healthy-looking gauge.
How to Fix a Vaillant F22 Fault: What You Can Check Yourself
Take these in order. If you’re unsure about any step, stop and call an engineer.
Step 1: Check the Pressure Reading
Look at the pressure gauge or display with the boiler cold and write the reading down. On many Vaillant boilers the pressure appears on the digital display, and some models need a button press to show it, so check your manual if you can’t see it. A cold reading of about 1 to 1.5 bar is normal for most boilers, so a figure well below that fits F22. If the gauge reads normal but F22 is showing, don’t keep topping up. That points to a sensor, pump or wiring fault, so call an engineer.
Step 2: Look for Leaks
Check under the boiler, along visible pipework and around each radiator valve for drips, damp patches, green or brown corrosion and water stains on floors or ceilings. Also look at the external PRV discharge pipe for dripping. A leak means topping up is only a temporary fix.
Step 3: Top Up the Pressure Through the Filling Loop
Only do this with the boiler cold, and follow the steps in your manual, because filling loops differ between models. The filling loop is usually a braided hose with a valve at each end, under the boiler, and some models have a built-in one behind a flap.
- Make sure both filling loop valves are closed. If the loop is removable, connect it.
- Open the valves slowly and watch the gauge. Stay with it the whole time. If you can’t hear water filling and the pressure doesn’t rise, the filling loop may be faulty or the mains supply may be off, so stop and call an engineer.
- Close both valves once the gauge reaches about 1 to 1.5 bar. Don’t go much higher.
- Disconnect a removable loop and check that the valves are closed. Wipe away any drips.
If you overfill, don’t leave it. Pressure above about 2.5 bar cold is too high and can make the PRV open. See boiler pressure too high for how to deal with it safely.
Step 4: Reset the Boiler Once
Follow the reset steps in your manual. If the boiler restarts and the pressure holds, you’re done. If F22 returns, stop. Another reset won’t fix a leak or a faulty part.
What Not to Do
Don’t open the boiler casing, touch the pressure sensor, pump, expansion vessel or PRV, or drain radiators to chase a leak. Don’t top up repeatedly without finding out why the pressure keeps falling. Vaillant recommends leaving F22 repairs to a qualified technician.
Gas Smell or Carbon Monoxide Alarm?
F22 is a water problem, not a gas one, but a gas smell changes everything. Leave the light switches and the reset button alone, let fresh air in if you can do so safely, shut the gas off at the meter, go outside and ring the National Gas Emergency Service on 0800 111 999.
A carbon monoxide alarm is a reason to switch the boiler off, open up the windows and doors and get everybody out of the building. Stay out until the property has been checked. Report it on 0800 111 999, and dial 999 if anyone has a headache, feels dizzy or sick, or has collapsed, because the gas line can’t give medical help.
When a Pressure Fault Needs an Engineer
- The code comes back after one top-up and one reset
- Pressure sinks again within a few days, or you find yourself refilling every few weeks
- There’s a wet patch or drip you can’t trace or stop
- Water is coming out of the PRV discharge pipe
- The display says F22 while the gauge shows a normal reading
- The filling loop on your model is unclear or isn’t covered in the manual
- Getting any further means taking the casing off
What Happens During a Repair Visit
The first job is tracing where the water is going. After that the engineer tests the filling loop and its valves, the PRV, the charge in the expansion vessel, the pressure sensor with its wiring, and the pump. Once the fault is cleared, they refill the system to the right pressure and check that it holds. The code only says the pressure is low, so the diagnosis is most of the work.
What a Vaillant F22 Repair Costs
Topping up the pressure yourself is free. When an engineer has to attend, labour is £95 an hour between 7AM and 5PM, £125 between 5PM and 9PM, and £160 overnight from 9PM to 7AM, all plus VAT. BeFix doesn’t charge a call-out fee, and parts are quoted on top once the cause is known.
A boiler that’s 10 or more years old and keeps losing pressure may be cheaper to replace than to keep repairing. Our boiler installation London page explains the options.
Related Vaillant Fault Codes
| Code | What It Points To | DIY? | Guide |
|---|---|---|---|
| F22 | Low water pressure | Frequently, with a filling loop top-up | This guide |
| F23 | Big gap between flow and return temperatures, usually poor circulation | In part, by bleeding radiators | Vaillant F23 fault code |
| F28 | No flame at start-up | Simple checks, then an engineer | Vaillant F28 fault code |
| F62 | Gas valve timing or a false flame signal | No | Vaillant F62 fault code |
| F83 | Temperature fails to rise after the burner lights | Depends on the cause | Vaillant F83 fault code |
How to Stop F22 Coming Back
Check the pressure gauge about once a month and always after bleeding radiators, and write down any top-ups. If you’re topping up more than a couple of times a year, get it checked, because that points to a leak or a failing expansion vessel. If F22 keeps returning, don’t keep topping up and resetting as a workaround. Have the boiler serviced every year so the sealed-system parts are tested before they fail. Many manufacturer warranties also expect an annual service.
Get Help With Falling Boiler Pressure
If the pressure won’t stay up, BeFix’s Gas Safe registered team can trace the leak or the failing part and repair it. We cover Vaillant sealed-system faults as part of our boiler repair in London service.
Appointments are often available the same day, depending on availability, with an engineer typically on site within 1 to 3 hours. Repairs carry a 12-month workmanship warranty. When you get in touch, give us the pressure reading, your boiler model and whether F22 came back after topping up.
To book a boiler repair, use the online form, ring 020 8058 4241 or email info@befix.co.uk. Phone lines are open 7AM to 10PM on weekdays and 9AM to 8PM at weekends. You’ll find us at 227B Nether Street, London N3 1NT.
FAQs
What does the Vaillant F22 fault code mean?
The boiler has detected no or insufficient water, or a pressure that is too low, so it has locked out for safety. The usual causes are a leak, recent radiator bleeding or a faulty part.
How do I fix a Vaillant F22 fault?
With the boiler cold, check the gauge and look for leaks, then top the pressure up to about 1 to 1.5 bar using the filling loop, following your manual. Reset once. If F22 returns, call a Gas Safe registered engineer.
What pressure should a Vaillant boiler be when cold?
About 1 to 1.5 bar for most models, rising to around 2 bar when heating is on. Your manual gives the exact range for your boiler.
Can I repressurise a Vaillant boiler myself?
Usually yes, using the filling loop with the boiler cold and following your manual. Don’t overfill, and stop if you find a leak or can’t see how your loop works.
Why does my Vaillant boiler keep losing pressure?
A slow leak, a leaking PRV or a failing expansion vessel are the usual reasons. If you need to top up every few weeks, the system has a fault that needs diagnosing.
Why does F22 show when the pressure gauge looks normal?
That can mean a faulty pressure sensor, its wiring or the pump. Don’t keep adding water. Call an engineer.
How do I tell if the pressure relief valve is faulty?
Look for water dripping from the external discharge pipe, or pressure that drops again soon after you top up. Replacing it is a job for a qualified engineer.
Is the F22 fault dangerous?
The lockout is a safety shutdown and low pressure itself isn’t an emergency. The risks come from ignoring a recurring leak or attempting repairs on sealed-system parts yourself. If you smell gas, leave and call 0800 111 999.
How much does it cost to fix a Vaillant F22 fault?
Topping up the pressure costs nothing. A BeFix visit is charged hourly: £95 in the daytime, £125 in the evening and £160 overnight, plus VAT, with no call-out fee. Parts are extra.
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