Viessmann Vitodens 100-W fault 463

What it means

Contaminated combustion air or flue gas recirculation detected.

Likely causes

1. Contaminated combustion air
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 flue system for contamination and flue gas recirculation
2. Check installation room and flue system for causes of deposits (e.g. laundry detergents, cleaning agents, toiletries, deposits in ventilation air supply/chimney)
3. Check the flue system for tightness (flue gas recirculation).