Vaillant F.22 Fault Code: Low Water Pressure Guide
The F.22 fault code on a Vaillant boiler means the boiler has shut down for safety because the water pressure inside the system has dropped too low.
What the F.22 fault code means
Your boiler needs water pressure between 1.0 and 1.5 bar to operate safely. When the pressure drops below 0.8 bar, the boiler shuts down to protect itself from damage. The F.22 code is Vaillant's low water pressure safety switch-off.
Possible causes of the F.22 fault
- Low system water pressure (below 0.8 bar) — The most common cause.
- Incorrect earth connection between cable harness and boiler
- Flow or return sensor (NTC) defective
- Fault in the cable or casing
- Black discharge via ignition cable, ignition plug or ignition electrode
Can you fix it yourself?
Yes — in most cases. The F.22 fault is one of the few boiler faults homeowners can safely fix:
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Check the pressure gauge — Look at the gauge on the front of your boiler. If the needle is below 1.0 bar, the system needs repressurising.
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Repressurise the system — Use the filling loop (a silver braided hose with two valves, usually under the boiler). Slowly open both valves and watch the pressure gauge. When it reads between 1.0 and 1.5 bar, close both valves.
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Reset the boiler — After repressurising, reset the boiler. The F.22 code should clear.
If the pressure keeps dropping after topping up, there is likely a leak or a faulty sensor that needs a Gas Safe engineer.
Need help with your Vaillant boiler?
Sanju's Heating covers Newbury, Basingstoke and Reading. Call us on 01635 74 50 40 or book online at sanjusheating.co.uk/book
Check our full Vaillant fault code guide for help with other Vaillant error codes.
