Vaillant F22 Fault: What It Means and How to Fix It

What does F22 mean on a Vaillant boiler?

F22 is Vaillant's low water pressure lockout, and it appears on ecoTEC, ecoFIT and most other Vaillant models. Sealed central heating systems run at pressure, typically between 1 and 1.5 bar when cold, and the boiler constantly monitors it. When the reading falls below roughly 0.5 bar, the boiler cannot circulate water safely, so it stops and shows F22. It is one of the most common codes any London engineer sees, it is not dangerous, and in most cases you can clear it yourself in five minutes without tools.

The pressure gauge tells you where you stand before you touch anything. On most Vaillants it is a small dial or digital reading on the front panel. Below 1 bar is low; below 0.5 bar is where F22 lives.

How to fix a Vaillant F22 fault in 5 steps

1. 1
   Turn the boiler off and let it cool.

   You are adding cold water to the system, and doing it cold gives an accurate reading.

2. 2
   Find the filling loop.

   On most Vaillant installations it is a silver braided hose beneath the boiler with a small valve at each end. Some ecoTEC models have built-in filling keys instead; your manual shows which you have.

3. 3
   Open both filling loop valves slowly.

   You will hear water flowing into the system. Watch the pressure gauge as it climbs.

4. 4
   Close both valves when the gauge reads 1.5 bar.

   Do not overfill; anything much above 2 bar cold is too high, and the pressure relief valve will dump the excess.

5. 5
   Turn the boiler back on.

   The F22 code should clear on its own or after pressing the reset button, and heating should resume normally.

If the display still shows F22 with the gauge reading 1.5 bar, the pressure sensor itself may be faulty, and that is an engineer's job.

Why does my Vaillant keep showing F22?

This is the question that matters, because F22 itself is only a symptom. If you are repressurising every few weeks, water is leaving the system, and it is going somewhere. The usual suspects, in order of frequency: a small leak in the pipework or at a radiator valve (often invisible, under floors or behind kitchen units), a pressure relief valve that has started weeping and is quietly dumping water down its outside discharge pipe, or an expansion vessel that has lost its air charge, which pushes pressure up and down with temperature until the relief valve vents it away.

Topping up forever does not fix any of these. It feeds them, and in the long run the constant introduction of fresh, oxygenated water accelerates corrosion inside the system. The honest rule: repressurising once or twice a year is normal life; once or twice a month is a leak, and a leak trace usually finds it within the hour.

Is it safe to keep resetting F22?

Resetting after repressurising is exactly what the boiler expects. What is not safe, for your wallet rather than your household, is the cycle of reset-and-ignore on a system that keeps losing pressure: running a boiler at chronically low pressure stresses the pump, and the underlying leak is doing slow damage to whatever it is dripping into. F22 will not hurt you. The floor under a hidden leak is another matter.

What does an F22 repair cost?

If the fix is a repressurise, it costs you five minutes. Where an engineer is needed, London prices run roughly as follows: a leak trace with repressurise from £95 to £220 depending on how well the leak hides, a pressure relief valve replacement £110 to £190, an expansion vessel recharge or replacement £120 to £380, and a pressure sensor swap £120 to £200. We quote fixed after diagnosis, and the diagnostic fee is waived when we do the repair.

Vaillant F22, quick answers