Viessmann Vitodens 100-W fault 352

What it means

Burner in a fault state because the combustion CO limit has been exceeded, often caused by flue gas path problems.

Likely causes

1. Combustion CO limit exceeded due to flue gas path leaks, back pressure, constrictions or blockages
2. Flue system leak causing flue gas recirculation
3. Incorrect gas flow pressure
4. Flue gas leakage
5. Blocked flue system
6. Simultaneous operation of boiler and air-extracting appliances
7. Negative pressure created by extractor hoods, extractors, air conditioning units, or central vacuum cleaning systems
8. Accumulation of condensate blocking flue system
9. External causes sealing the flue system
10. Inadequate supply of combustion air
11. Building modifications affecting cable/pipework routing, cladding or partitions

Where to start

1. Check entire flue gas path for leaks.
2. Check for flue gas back pressure caused by water pocket (if flue system fall is insufficient).
3. Check for constrictions.