Viessmann VITOTRONIC 300 Installation And Service Instructions Manual page 66

Function Description
Heating Circuit Control Unit of the Vitotronic 300-K
DHW temperature
Priority control
H With priority control: (code "A2:2" in the "Heating
circuit..." group):
The set supply temperature is set to 32° F (0° C)
during DHW tank heating. The mixing valve closes and
the heating circuit pump is switched off.
H Without priority control: The heating circuit control unit
continues to operate with the same set value.
Heating circuit pump logic (economy mode)
The heating circuit pump is switched off [set supply
temperature set to 32° F (0° C)] if the outside
temperature exceeds the value selected via coding
address "A5" in the "Heating circuit..." group.
Extended economy mode
The heating circuit pump is switched off [set supply
temperature set to 32° F (0° C)] if one of the following
criteria is met:
H The adjusted outside temperature exceeds the value
selected via coding address "A6" in the "Heating
circuit..." group.
H The heating circuit pump can be switched off for a time
calculated by the control unit when changing over from
heating mode to reduced mode.
Requirement:
– There is no risk of frost.
– Coding address "B0" in the "Heating circuit..." group
must be set to 0.
The idle period can be individually adjusted via coding
address "A9" in the "Heating circuit..." group.
Note: If, during the pump idle period, the system is
switched over to heating mode or the set room
temperature is increased, the heating circuit pump
is switched on, even if the period has not yet
expired.
H The actual room temperature exceeds the value
selected via coding address "B5" in the "Heating
circuit..." group.
H The mixing valve has been closed for 12 min. (mixing
valve economy function, coding address "A7" in the
"Heating circuit..." group).
66
Vitotronic 300, GW5B & MW1B Installation and Service
(continued)
System dynamics
You can influence the control characteristics of the mixing
valves via coding address "C4" in the "Heating circuit..."
group.
Central control
Central control for a heating circuit can be programmed
via coding address "7A" in the "General" group.
The heating and holiday program then applies to all
additional heating circuits of the system.
For these heating circuits, when the heating and holiday
program is enabled, "Central control" is displayed. Any
holiday programs that may have been set will be deleted.
Party and economy modes cannot be enabled on all
control units.
Frost protection
The supply temperature is maintained in accordance with
the heating curve for the reduced set room temperature,
but at min. 50° F (10° C).
A variable frost limit can be set in accordance with coding
address "A3" in the "Heating circuit..." group.