Vaillant F.22: low water pressure in the system
Checked against Vaillant's own documentation: Vaillant: boiler fault codes list and 8 more sources. Last reviewed October 2026. How we check
You can usually fix this
The water pressure in your heating system has dropped below what the boiler needs, so it has stopped to protect itself. This is the most common Vaillant code and usually something you can fix in a few minutes by topping up the system.
Recommended pressure when cold for Vaillant boilers: 1.0 to 2.0 bar.
What you can safely do
- Let the heating cool down. Vaillant's figure of 1.0 to 2.0 bar is for a cold system.
- Find the filling loop or filling tap, usually under the boiler. Vaillant's instructions say to ask your installer to show you where it is if you're not sure. If yours is a detachable hose, connect it as your manual shows.
- Open all the radiator valves.
- Open the filling tap slowly and let water in until the gauge or display reads between 1.0 and 2.0 bar, then close it fully.
- Bleed the radiators, then check the pressure again and top up a little more if it has dropped.
- Clear F.22 using the reset key as your manual describes.
Call a Gas Safe engineer if
- The pressure drops again within a few days. Water is escaping somewhere.
- You can see water dripping from the boiler or pipework.
- F.22 comes back even though the pressure reads between 1.0 and 2.0 bar.
- You can't find the filling loop or aren't sure how to use it.
Which Vaillant boilers show F.22
| Model | What Vaillant's manual says | Source |
|---|---|---|
| ecoTEC pro | Switches off when the pressure falls below 0.5 bar. The operating instructions tell you to refill to 1.0 to 2.0 bar when cold. | Vaillant ecoTEC pro operating instructions (0020244996_01, 2017) |
| ecoTEC exclusive | Switches off below 0.5 bar and the display shows F.22. | Vaillant ecoTEC exclusive installation and maintenance instructions (0020193968_05, 2021) |
| ecoTEC sustain | Switches off below 0.3 bar and stores F22 in its fault list. | Vaillant ecoTEC sustain 24, 28, 34 installation and maintenance instructions (0020253094_06, 2021) |
| ecoFIT pure | The operating instructions say to check the pressure on the display and refill to 1.0 to 2.0 bar if it's low. | Vaillant ecoFIT pure 825–835 combi operating instructions (0020230532_03, 2019) |
| ecoTEC plus | Listed in the fault code table as low water pressure. | Vaillant ecoTEC plus installation and maintenance instructions: overview of fault codes |
What Vaillant's online fault list says
Vaillant's online fault code list treats F.22 as a job for an expert. It lists the causes an engineer would check: too little water in the system, a loose or faulty pressure sensor or its wiring, the pump, a solenoid valve, or the boiler's internal expansion vessel.
Vaillant's operating instructions, on the other hand, show you how to refill the system yourself. So top up once, following your manual. If F.22 comes back, one of the other causes is likely, and that needs a Gas Safe registered engineer.
If the pressure keeps dropping
Vaillant says low pressure usually means water is escaping, most often around plumbing fittings. Look for damp spots or rust marks around your radiators, and flaking wallpaper. Get the leak fixed before you top up again.
Worcester Bosch says needing to top up once or twice a year is normal. If you're doing it more often than that, water is escaping. Use our pressure checker to compare your reading with Vaillant's range.
Applies to Vaillant ecoTEC pro, Vaillant ecoTEC exclusive, Vaillant ecoTEC sustain, Vaillant ecoFIT pure, Vaillant ecoTEC plus. Codes can differ between models, so check your manual.