F.11 / F11 — Vaillant ecoTEC exclusive 832/838
What it means: The return temperature sensor circuit is shorted, so the electronics are receiving a false reading.
Typical causes
- Sensor plug shorting to the casing
- Short circuit in the wiring loom
- Faulty sensor
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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