How to Fix Vaillant F22 Fault Code (UK)
Vaillant showing F22 — Low water pressure. UK diagnosis, likely spare (expansion vessel / filling loop) and step-by-step reset.
What the code means
F22 on a Vaillant indicates low water pressure. The boiler locks out to protect the heat exchanger and, on gas faults, to comply with the Gas Safety (Installation and Use) Regulations. Always reset to confirm the code is live, not historical.
Likely spare
The most common fix is the expansion vessel / filling loop. Check the exploded diagram against the GC number on the data plate before ordering — Vaillant revised parts on Vaillant units mid-production.
Fix procedure
Top up to 1.5 bar via key. If loses pressure, check EV via schrader.
Log the fault and reset. If the code returns within 24 hours, escalate to full electrical diagnosis with a manometer and multimeter.
Frequently asked questions
- Can I reset F22 myself?
- You can press the reset button up to 3 times. If F22 returns, the boiler needs a Gas Safe engineer — it is illegal to repair gas components without registration.
- Is the part covered under warranty?
- Vaillant standard warranty is 2–10 years depending on model. Registered installations get the full term. Check the sticker inside the case.
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