F.0 / F0 — Vaillant ecoTEC exclusive 832/838
What it means: The electronics cannot read the flow temperature sensor because its circuit is broken.
Typical causes
- Faulty sensor
- Damaged sensor cable
- Poor connection at the sensor plug
- Poor connection at the control board plug
When to treat it as unsafe
Treat as unsafe if the boiler keeps firing when it should not, or if other fault codes appear with this one.
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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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