Viessmann Vitocrossal 300 CA3 2.5 Installation And Service Instructions Manual page 134

Function Description
DHW Tank Temperature Control
134
Vitocrossal 300 CA3 Series 2.5 to 6.0 Installation/Service
(continued)
Tank temperature control with 2 tank temperature sensors
Coding "55:2" in the "DHW" group;
Tank temperature sensor 1 enables the DHW pump and
is evaluated for stop conditions during the pump delay
off time.
Tank temperature sensor 2:
Tank heating will start early if a lot of hot water is drawn
off. Tank heating will terminate early if no hot water is
drawn off.
DHW tank goes cold:
H Set value -5°F (–2.5 K), change at coding "59"
or...
H Actual DHW temperature at sensor 2 < set DHW
temperature x factor for start time (adjustment at
coding "69")
The DHW tank is hot:
H set value 5°F (2.5 K)
and...
H Actual DHW temperature at sensor 2 > set DHW
temperature x factor for stop time (adjustment at
coding "68")
Coding "55:3" in the "DHW" group;
tank temperature control tank loading system
The DHW tank goes cold [set value -5°F (–2.5 K); change
at coding "59"]:
H The set boiler water temperature is set 36°F (20 K)
higher than the set DHW temperature (adjustable via
coding "60").
H The primary pump in the tank loading system starts.
H The 3-way mixing valve opens and then regulates to
the specified set value.
H The DHW pump cycles (briefly switches on and off)
until the set supply temperature has been reached [set
DHW temperature +10°F (+5 K)].
Then it runs constantly. If, during heating, the actual
value falls below the required set temperature, the DHW
pump will temporarily cycle again.
The DHW tank is hot:
H Tank temperature sensor 1:
Actual value ≥ set value
and...
Tank temperature sensor 2:
Actual value > set value -3°F (–1.5 K):
H The set boiler water temperature is reset to the
weather-compensated set value.
H The DHW pump stops immediately when the 3-way
mixing valve is fully opened.
or...
H The DHW pump stops after expiry of the delay off time
that is selected at coding "62".