F.22 / F22 — Vaillant ecoTEC exclusive 832/838
What it means: The boiler has detected a dry-fire condition, meaning it is heating with too little water.
Typical causes
- Insufficient water in the boiler
- Faulty water shortage switch
- Damaged cable to the pump or the switch
- Pump seized or faulty
- Pump delivering too little flow
When to treat it as unsafe
Treat as unsafe if the boiler has fired with little or no water in it, and do not return it to service until the cause is found.
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NwadFix is not affiliated with or endorsed by Vaillant. Manufacturer and model names are used only to identify the appliances an entry refers to.
Last reviewed: 13 October 2026 by a Gas Safe Engineer
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