Vaillant F22 Fault Code: Not Enough Water Pressure

Why has my Vaillant shut down with F22?

A sealed heating system holds its water under pressure, and the boiler reads that pressure through a sensor. On ecoTEC plus models, Vaillant's installation manual says the pressure figure starts flashing on the display once it falls below 0.8 bar. The point where the boiler switches off and shows F22 depends on the generation: below 0.5 bar in the manuals up to 2021, and at 0.3 bar or less in the 2023 edition for the newest models.

So if you catch the flashing number before F22 appears, a top-up now saves you a cold evening later.

Older ecoTEC plus installer manuals list three causes behind the code: the system genuinely has too little water, the water pressure sensor has failed, or the plug and cable to the pump or pressure sensor have worked loose. The newest manual adds a faulty internal expansion vessel and, on boilers that have one, a faulty automatic filling valve. Too little water is by far the most common, and it is the only one you can deal with yourself.

How do I top up the pressure and clear F22?

Vaillant's own advice is that F22 with a gauge under 1 bar can be solved without an engineer if you are competent to do it. Turn the heating off and let the radiators cool, because a hot system reads higher than a cold one.

• Find the filling loop under the boiler. On many ecoTEC plus combis it is built in; older boilers use a braided hose between two small taps.
• Open the valves slowly and watch the pressure rise. Stop between 1 and 1.5 bar.
• Close both valves fully. On an external hose loop, the manual says to disconnect it afterwards.
• Press reset once and let the boiler run through its start-up.

Do not overfill. Pressure rises as the water heats up, and at 3 bar the pressure relief valve opens and dumps water through the pipe outside. Fill a cold system well past 1.5 bar and the first hot evening can take it there, and you are back where you started. See lowering boiler pressure if you overshoot.

Why does F22 keep coming back?

Water does not leave a sealed system by itself. If you are topping up every few days, it is escaping somewhere, and the usual places are the pressure relief valve (check the copper pipe outside for a drip or a damp patch below it), a weeping radiator valve, a leak under the floor, or an expansion vessel that has lost its charge and makes the relief valve lift every time the heating warms up.

Bleeding radiators also lowers the pressure, so a top-up after bleeding is normal. Needing one every week is not. Our guide to pressure that keeps dropping goes through the order to check them in.

If the gauge reads 1 bar or more and the boiler still shows F22, the water is fine and the reading is not. That points to the pressure sensor or its wiring, which is inside the casing.

What will an engineer check, and what does it cost?

Vaillant's fault table tells the engineer to check the plugs and cables to the pump and pressure sensor, the sensor itself and the pump, then run check programme P.0 to purge air from the boiler. A leak search comes first if the system keeps emptying.

The water pressure sensor used on many ecoTEC models (part 0020059717, though check it against your boiler) is an inexpensive part, typically well under £50 from parts suppliers, so most of the bill is labour. Finding and fixing a hidden leak costs more, and a failed expansion vessel inside the boiler is a bigger job again.

Our visit starts with the £60 call-out, and the repair price is agreed with you on site before any work starts. If you want someone to find where the water is going, book a Vaillant boiler repair.