Viessmann Vitodens 100-W fault 694
Burner in a fault state, signal comparison deviation, flue gas high limit safety cut-out
Gas boilerWhat it means
Burner fault state caused by a signal comparison deviation relating to the flue gas high limit safety cut-out sensor.
Likely causes
- Signal comparison deviation, flue gas high limit safety cut-out
- Faulty sensor
- Faulty plug-in connection or lead to sensor
- Flue system leak causing flue gas recirculation
- Incorrect gas flow pressure
- Flue gas leakage
- Blocked flue system
- Simultaneous operation of boiler and air-extracting appliances
- Negative pressure created by extractor hoods, extractors, air conditioning units, or central vacuum cleaning systems
- Accumulation of condensate blocking flue system
- External causes sealing the flue system
- Inadequate supply of combustion air
- Building modifications affecting cable/pipework routing, cladding or partitions
Where to start
- Check plug-in connection and lead to sensor
- Check sensor
- Check the flue system for tightness (flue gas recirculation).
The full answer, free
- 17 more checks in order
- The readings and component tests from the manual
- How to put it right, step by step
- The manual page for this fault (page 87), right under the answer
Safety: Isolate gas and power before you open the case. If you have been into the gas side, do a tightness test, and a combustion and flue check before you hand back. Gas Safe (UK) or RGI (Ireland) work only.
From the Viessmann manual for the Vitodens 100-W. Check the model on the data plate before you order parts.