Vaillant F22 Fault Code: Causes & What to Do

Vaillant F22 fault code? F22 means the boiler has detected low water pressure in the heating system. In many cases, the pressure gauge will be below the boiler’s normal operating range.

The immediate problem may sometimes be solved by repressurising the system according to your Vaillant instructions, but if the pressure keeps falling, the boiler may have a leak or another pressure-related fault that needs investigating.

F22 can also be linked to pressure-sensor, wiring, pump or expansion-vessel problems, so do not assume that topping up the boiler will always solve it.

What Does the Vaillant F22 Fault Code Mean?

Vaillant describes F22 as low water pressure in the system.

The boiler needs sufficient water and pressure to circulate heat safely around the heating system. If the pressure drops too far, the appliance can stop operating and display F22.

You may notice:

• F22 on the boiler display;
• no central heating;
• no hot water on a combi boiler;
• a pressure reading below the normal range;
• the boiler returning to F22 after being topped up.

Vaillant F22 Fault Code: What Should I Check First?

Start with the boiler pressure display.

Vaillant states that many of its sealed systems normally operate at around 1 to 1.5 bar when cold, although you should always check the instructions for your specific boiler model.

If the pressure is below 1 bar, low system pressure may explain the F22 fault.

If the pressure appears normal but F22 is still displayed, do not keep adding water. A pressure sensor, wiring or another boiler component may need checking.

For a general explanation of boiler pressure, see:

Normal Boiler Pressure & Pressure Adjustment

5 Common Causes of a Vaillant F22 Fault

1. The Heating System Has Lost Pressure

The most obvious cause is that the sealed heating system simply does not contain enough water pressure.

This may happen gradually over time or more quickly if water is escaping somewhere.

Check the pressure shown on the boiler when the system is cold.

If it is below the recommended range, the system may need repressurising according to the instructions for your particular Vaillant boiler.

2. There Is a Leak in the Heating System

If you repressurise the boiler and the pressure falls again, water may be escaping somewhere in the system.

Without removing any boiler covers, check visible areas such as:

• radiator valves;
• visible pipe joints;
• the floor around radiators;
• accessible heating pipework;
• the area beneath the boiler.

A very small leak may leave only staining, dampness or corrosion rather than a large puddle.

If your boiler is visibly leaking, see:

Boiler Leaking Water? Causes & What to Do

3. The Pressure Sensor Is Faulty

Vaillant lists the water-pressure sensor as another possible cause of F22.

This matters because the boiler may sometimes report a pressure problem even when the actual water pressure is not obviously low.

If the gauge or display shows more than around 1 bar but the boiler still reports F22, do not keep adding water to the system.

The pressure sensor and its electrical connections may need professional testing.

Diagnostic point: a fault code tells us what condition the boiler has detected. It does not always prove which component has failed.

4. Wiring or Pump Problem

Vaillant also lists loose, disconnected or faulty wiring associated with the pump or pressure sensor as possible causes of F22.

On some systems, a pump problem can also be involved.

These are internal boiler or heating-system checks and should not be attempted by removing the appliance casing yourself.

An engineer can use the fault code together with the pressure reading and boiler behaviour to work out whether the problem is genuine low pressure or an electrical or circulation fault.

5. Expansion Vessel Problem

The expansion vessel helps control changes in pressure as the heating water warms up and cools down.

If the expansion vessel is not working correctly, the boiler pressure may rise too far when hot, discharge water through the pressure-relief system and then fall too low once the system cools.

This can create a pattern where you repeatedly:

1. top the boiler up;
2. run the heating;
3. see the pressure rise;
4. later find the pressure low again;
5. eventually see F22 return.

If your pressure repeatedly moves between high and low readings, the underlying pressure-control problem should be diagnosed rather than continually adding more water.

How Do I Repressurise a Vaillant Boiler With F22?

If the pressure is genuinely below the recommended range, Vaillant advises that some homeowners who are competent and comfortable doing so can repressurise the system using the boiler’s filling arrangement.

The exact method depends on the Vaillant model.

Some boilers use an external filling loop, while others may have a different filling arrangement.

Always:

• check the correct Vaillant manual for your boiler;
• identify the correct filling controls;
• increase the pressure slowly;
• stop when the recommended cold pressure is reached;
• fully close the filling controls afterwards.

Do not copy a filling procedure from a different boiler model.

If you’re unsure what the filling loop is, read:

Boiler Filling Loop & Valve Guide

What Pressure Should a Vaillant Boiler Be?

Vaillant states that many systems normally sit around 1 to 1.5 bar when cold.

The pressure normally rises somewhat when the heating warms up because the water expands.

The exact recommended level can vary by model, so the user manual remains the best reference for your particular boiler.

If the pressure is below 1 bar and F22 is displayed, repressurising may restore normal operation.

If the pressure is already above 1 bar and F22 remains, Vaillant recommends professional investigation rather than continuing to fill the system.

Why Does F22 Come Back After I Repressurise the Boiler?

This is one of the most important F22 symptoms.

If you restore the pressure and the boiler works, but F22 returns a few hours or days later, the system is probably losing pressure for a reason.

Possible causes include:

• a radiator or pipework leak;
• an internal boiler leak;
• pressure-relief discharge;
• an expansion-vessel problem;
• a pressure-sensor or related fault.

Continually topping the boiler up is not a long-term solution.

See our detailed guide:

Why Does My Boiler Pressure Keep Dropping?

Why Does the Pressure Drop Overnight?

Boiler pressure normally changes slightly between a hot and cold heating system.

If the pressure falls substantially overnight and continues dropping each day, however, the system may be losing water or have another pressure-related fault.

Make a note of:

• the pressure when the system is cold;
• the pressure when the heating is hot;
• how quickly it falls;
• whether you can see any leaks;
• whether an outside discharge pipe is dripping.

That information can help an engineer diagnose the problem.

Can Bleeding Radiators Cause F22?

Yes, potentially.

Bleeding a radiator releases trapped air, but the process can also reduce system pressure.

Vaillant specifically advises checking the boiler pressure after radiators have been bled because an F22 fault can appear if the pressure becomes too low.

If the pressure falls only after bleeding radiators, the system may simply need to be returned to the correct pressure.

If the pressure keeps dropping afterwards, there may be another problem.

Can a Leak Cause Vaillant F22?

Yes.

If water leaves a sealed heating system, the pressure will fall with it.

A leak can be:

• around a radiator valve;
• at a pipe joint;
• inside the boiler;
• from another heating-system component;
• hidden beneath floors or behind walls.

Not every pressure leak creates an obvious puddle, especially when the loss is slow.

Can I Reset a Vaillant F22 Fault?

If the boiler manufacturer instructions allow a normal reset, you can follow the specified procedure.

However, resetting alone does not correct low system pressure.

If the boiler pressure is too low, the water pressure needs to be restored first according to the manufacturer’s instructions.

If F22 repeatedly returns after the pressure has been corrected, arrange professional diagnosis.

Should I Keep Topping Up a Vaillant Boiler?

No, not repeatedly.

An occasional pressure adjustment can sometimes be normal, particularly after radiator work or bleeding.

Having to refill the boiler every few days or every week suggests the pressure is being lost somewhere.

Repeatedly adding fresh water without finding the cause can mask the problem rather than repair it.

Can I Fix Vaillant F22 Myself?

If the only issue is genuinely low system pressure, and you understand the correct filling procedure for your particular Vaillant boiler, repressurising may be a normal homeowner task.

You should arrange professional help if:

• F22 remains even though the pressure is normal;
• the pressure immediately falls again;
• you cannot identify the correct filling controls;
• the boiler is leaking;
• the pressure rises dramatically when the heating runs;
• a pressure sensor, pump or expansion vessel is suspected;
• you would need to remove the boiler casing.

Do not open the boiler casing to investigate F22 yourself.

How Much Does It Cost to Fix Vaillant F22?

There is no single F22 repair price because the solution depends on the actual cause.

If the system simply needs normal repressurisation, there may be no failed boiler component at all.

If pressure keeps falling, the repair could instead involve:

• a heating-system leak;
• a boiler leak;
• a pressure sensor;
• an expansion vessel;
• a pump or wiring problem;
• another pressure-related component.

The sensible approach is to diagnose why the pressure is low before pricing the repair.

Does F22 Mean I Need a New Vaillant Boiler?

No.

F22 on its own does not mean the boiler needs replacing.

Many low-pressure faults can be repaired once the reason for the pressure loss has been identified.

Replacement becomes worth comparing when an older boiler has several significant faults or the confirmed repair is substantial relative to the condition of the appliance.

When Should I Call a Boiler Engineer?

Arrange professional diagnosis if:

• F22 keeps returning after repressurising;
• the pressure drops quickly;
• F22 appears even though pressure is above 1 bar;
• the boiler or heating system is leaking;
• pressure rises dramatically when the heating runs;
• water is being discharged outside;
• the filling loop does not appear to work correctly;
• the boiler remains locked out.

For professional fault diagnosis, visit:

Boiler Repairs

Vaillant F22 Fault in Cardiff?

If you’re in Cardiff and your Vaillant boiler is showing F22, repeatedly losing pressure or failing to provide heating and hot water, visit:

Boiler Repair in Cardiff

When booking, tell us:

• your Vaillant boiler model;
• the F22 fault code;
• the current pressure reading;
• how quickly pressure falls after topping up;
• whether you can see any water leaks;
• whether pressure rises significantly when the heating is running.

Quick Questions

What does F22 mean on a Vaillant boiler?

F22 means the boiler has detected low water pressure in the heating system.

What pressure causes Vaillant F22?

Vaillant advises that many systems normally operate around 1 to 1.5 bar when cold. F22 can occur when the pressure falls below the boiler’s required operating range.

Can I fix F22 by topping up the boiler?

If the system pressure is genuinely low, repressurising according to your Vaillant user instructions may clear the fault. If F22 returns, the cause of the pressure loss should be investigated.

Why does my Vaillant boiler keep showing F22?

Repeated F22 faults may be caused by ongoing pressure loss, a leak, expansion-vessel problems, pressure-sensor faults, wiring or another heating-system issue.

Can a faulty pressure sensor cause F22?

Yes. Vaillant lists a faulty water-pressure sensor and associated wiring among the possible causes of F22.

Can an expansion vessel cause F22?

Yes. Vaillant also lists an internal expansion-vessel fault as a possible cause. Expansion problems can sometimes create large pressure swings between a hot and cold system.

Need Help With a Vaillant F22 Fault?

Let’s Heat can investigate recurring F22 faults, low boiler pressure, leaks and pressure-related boiler problems.

You do not need to know which component has failed before booking.

Book Boiler Repair →

Sources Checked

This guide has been checked against current Vaillant homeowner and fault-code guidance.

Vaillant – Official Boiler Fault Codes

Vaillant – What Pressure Should My Boiler Be?

Vaillant – Low Boiler Pressure Guidance