Error code
Vaillant Boiler Fault Code F22
The heating system pressure is too low The most likely cause is pressure dropped below the normal operating range. Check first: look for obvious signs of water around radiators, pipework, or the boiler area without removing the casing.
Quick answer
F22: what does it mean and how to fix
What does it mean?
The heating system pressure is too low
How to fix first
Check the pressure gauge or display against the range stated in the Vaillant user manual.
Why is this happening?
Pressure dropped below the normal operating range
When should I call an engineer?
Arrange a qualified heating engineer if pressure repeatedly drops, you find a leak, the filling loop does not restore pressure normally, or the boiler continues showing F22 after correct repressurising.
What does this error code mean?
Vaillant boiler fault code F22 usually means the boiler has detected insufficient water pressure in the sealed heating system and has locked out to protect itself. This is different from Ideal F9-style circulation faults: F22 starts with the pressure reading, although leaks or circulation problems can sit behind repeated pressure loss.
This code usually points to low system water pressure, recent pressure loss, or a leak in the heating circuit.
Start with this safe check: Check the pressure gauge or display against the range stated in the Vaillant user manual. If the code returns, the fault worsens, or the appliance does not behave normally, arrange a qualified heating engineer if pressure repeatedly drops, you find a leak, the filling loop does not restore pressure normally, or the boiler continues showing F22 after correct repressurising.
Symptoms users may notice
- The boiler may lock out and stop heating or hot water demand.
- The pressure gauge may show below the normal operating range.
Why is this happening?
- Pressure dropped below the normal operating range
- Recent radiator bleeding or maintenance
- Ongoing water loss from a leak
- Filling loop not fully closed or not used correctly
- Expansion vessel or pressure relief issue if pressure repeatedly drops
What this usually points to
This code usually points to low system water pressure, recent pressure loss, or a leak in the heating circuit.
How to fix this safely
- Check the pressure gauge or display against the range stated in the Vaillant user manual.
- Look for obvious signs of water around radiators, pipework, or the boiler area without removing the casing.
- If your model allows user repressurising, follow only the official filling loop method in the manual.
- Stop if pressure rises too high, drops again quickly, or you are unsure which valves to use.
What not to do
- Do not keep topping up pressure if it drops again quickly or if you can see signs of a leak.
- Do not remove the boiler casing to look for the leak source.
Common misdiagnoses
- This can be treated as a simple top-up issue, but repeated F22 often means pressure loss needs investigation.
Reset steps
- Reset the boiler only after pressure has been restored to the correct range using the approved method.
- Check whether the pressure remains stable when the heating runs.
- Do not keep resetting if the pressure immediately falls again or F22 returns.
Intermittent vs persistent faults
A one-off F22 after radiator bleeding may be resolved by approved repressurising, but repeated pressure drops should be treated as persistent.
When to call an engineer
Arrange a qualified heating engineer if pressure repeatedly drops, you find a leak, the filling loop does not restore pressure normally, or the boiler continues showing F22 after correct repressurising.
Safety warning
Do not remove the boiler casing or attempt internal repairs. Use only the manufacturer-approved repressurising method, and book a qualified heating engineer if pressure keeps falling.
Useful hub links
Related low-pressure fault codes
Relevant guide
Frequently asked questions
Can I keep resetting a Vaillant boiler with F22?+
No. Reset only after the pressure has been corrected using the approved user method. If F22 returns, the pressure loss needs investigation.
Is Vaillant F22 just low pressure?+
It usually starts as a low-pressure lockout, but repeated F22 can indicate a leak, filling loop issue, expansion vessel problem, or another fault.
What pressure should I top it up to?+
Use the range in your Vaillant manual for your exact model. Do not guess, and stop if the pressure climbs too high.
How is F22 different from a circulation fault?+
F22 is triggered by low system pressure. Circulation faults focus more on whether water is moving properly through the boiler and heating circuit.
What does F22 mean on a Vaillant boiler?+
F22 usually means the heating system pressure is too low. If it repeats after one safe retry, treat it as a persistent fault.
How to fix F22 on a Vaillant boiler?+
Check the pressure gauge or display against the range stated in the Vaillant user manual. Look for obvious signs of water around radiators, pipework, or the boiler area without removing the casing. Stop and escalate if the code returns immediately.
Why is F22 happening on my Vaillant boiler?+
The most common reasons are Pressure dropped below the normal operating range, Recent radiator bleeding or maintenance, Ongoing water loss from a leak. Repeated returns usually mean the underlying component or system still needs attention.