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Cascade communication loss (emergency operation)
What happens, in order
- Boilers in a CAN bus cascade normally follow the lead boiler
- If communication to the lead boiler fails, each boiler keeps using the last value it received for 60 seconds
- After 60 seconds each boiler runs on its own to a fixed emergency flow setpoint (only if emergency operation is enabled)
- Boiler frost protection monitoring stays active the whole time (boiler temperature below 41 F / 5 C)
Timings and thresholds
| Item | Value |
|---|---|
| Changeover time | 60 s |
| Emergency setpoint default | 140 F (60 C), range 32-176 F |
| Emergency operation default | disabled |
Applies to: Vitodens 200-W B2HE cascades
Models
More Viessmann boiler sequences
- Storage tank (cylinder) heating · Domestic hot water
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Source: Viessmann Vitodens 200-W B2HE service manual (DHW and boiler function parameters, cascade emergency operation). Written in our own words; timings can differ by model and software version, so check the manual for your exact unit.
For licensed technicians. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Shut off power and gas before servicing, never bypass a safety control, and follow the manufacturer’s manual for the exact model; it and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.