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The Vaillant F22 fault indicates that your boiler has detected low or no water pressure. As a safety measure, the boiler shuts down until the pressure returns to a safe operating level.

Low pressure is often caused by a simple loss of system pressure, but it can also point to a leak or a faulty component.

Vaillant boilers generally operate best at around 1.5 bar when cold. Many models display the F22 fault code once pressure falls to around 0.3 bar or below, though the exact trigger point varies between boiler ranges — check your model's manual for the precise figure.

Vaillant F22 boiler fault code complete guide with two Vaillant boilers on a white background
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How to Identify the Vaillant F22 Fault

The fault appears as F22 or F.22, depending on your boiler model. You may also notice:

  • No heating or hot water
  • Low reading on the pressure gauge
  • Boiler repeatedly locking out
  • Pressure continuing to fall after topping up

If the pressure keeps dropping, there is usually an underlying problem that needs investigating.


Common Causes of the Vaillant F22 Fault

The most common causes are:

  • Low system water pressure.
  • Air trapped after bleeding radiators or carrying out maintenance.
  • A faulty pressure sensor giving incorrect readings.
  • A leak somewhere within the heating system.
  • A failed expansion vessel or other internal boiler component.

If the pressure only drops occasionally, repressurising the system may solve the issue. If the fault returns regularly, book an inspection.

For a complete overview of Vaillant error codes and what each one means, see our Vaillant boiler fault codes guide.

How to Repressurise Your Boiler Safely

If your boiler pressure is low and there are no obvious leaks:

  • Turn the boiler off and allow it to cool.
  • Locate the filling loop.
  • Open both filling loop valves slowly.
  • Watch the pressure gauge.
  • Close both valves once the pressure reaches around 1.5 bar.
  • Restart the boiler.

If your model uses a removable filling loop, reconnect and remove it according to the manufacturer's instructions.

If the pressure quickly drops again, stop topping it up and arrange a professional inspection.

When the F22 Fault Needs a Heating Engineer

Boiler leak

Close-up of a Vaillant boiler showing the F22 fault code with water leaking from the pipe underneath.

A leaking heating system or boiler should always be investigated by a qualified engineer. Simply adding more water will not solve the underlying problem.

Faulty pressure sensor

If the pressure gauge appears normal but the boiler still shows an F22 fault, the pressure sensor or related components may need testing or replacing.

Failed boiler components

Internal faults such as a failed expansion vessel or other damaged components require diagnosis and repair by a Gas Safe registered engineer.

If you think your boiler is becoming unreliable or repeated repairs are needed, replacing the appliance may be the more cost-effective long-term option. If the F22 fault keeps returning after repressurising the system, you may need a professional boiler repair in London to identify the underlying cause.

What Affects the Cost of an F22 Repair?

Repair costs depend on the cause. Simple issues such as restoring system pressure may involve little or no repair work.

Where a leak, pressure sensor or expansion vessel needs repairing or replacing, the cost depends on the component and how much access it needs. A Gas Safe engineer can confirm the exact cost once the fault has been diagnosed.

If the boiler has multiple faults or is beyond economical repair, a qualified engineer can advise on replacement as an alternative.

Need Help With a Vaillant F22 Fault?

If your Vaillant boiler keeps displaying the F22 fault, don't ignore it — repeated pressure loss usually indicates an issue that needs diagnosing. Our Gas Safe engineers repair Vaillant boilers across London and can identify whether the fault is caused by a leak, pressure sensor, expansion vessel or another component.

Request a quote today and we'll explain your repair options and get your heating back up and running safely.

Get lightning fast quotes. Alternatively, we do offer site surveys where needed.