HVACopediaViessmann · Boiler · Domestic hot water
Storage tank (cylinder) heating
What happens, in order
- Tank temperature falls below the target DHW temperature by the start point and DHW heating begins
- DHW heating priority parameter (933.3 etc.) decides if the heating circuit pump and mixing valve are held off during tank heating
- Boiler heats until the tank reaches 5 F above the target (stop point)
- If the maximum DHW heating time is exceeded, heating stops even if the target is not reached
- After that the boiler must wait the minimum delay before it heats the tank again, even with a demand
- When tank heating ends the circulation pump runs on
Timings and thresholds
| Item | Value |
|---|---|
| Start point (1085.0) | default 2.5 K (5 F) below target, adjustable 1.0-10.0 K |
| Stop point | 2.5 K (5 F) above target |
| Max DHW heating time (1087.0) | default 60 min, adjustable 1-240 min |
| Delay before next DHW heating (1087.1) | default 60 min, adjustable 60-240 min |
| Circulation pump run-on (534.0) | default 120 s, 0-900 s, do not set below 120 s |
Applies to: Vitodens 200-W B2HE 85, 120, 150, 199
Models
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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.
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