Function Description; Constant Temperature Control Unit - Viessmann Vitodens 200 Service Manual

Function description

Constant temperature control unit

Heating mode
The set boiler water temperature will
be maintained in the heating and
DHW operating program G, when a
demand is raised by the room tem-
perature dependent clock thermostat.
If no demand is received, the boiler
water temperature will be held at the
defaulted frost protection tempera-
ture. The burner control unit limits the
boiler water temperature: Through the
control thermostat to 74 °C, and
through the electronic temperature
limiter to 82 °C. The temperature lim-
iter in the safety chain locks out the
burner control unit at a boiler water
temperature of 100 °C.
96
DHW loading with gas fired combi-
nation boilers
If the flow switch recognises that
DHW is drawn off (> 3 l), the burner
and circulation pump are switched
ON, and the three-way valve changes
over to DHW loading (display symbol
w). The burner modulates to reach
the DHW outlet temperature and is
limited on the boiler side by the tem-
perature limiter (82 ºC). With acti-
vated comfort operation, the plate
heat exchanger will be held to a
standby temperature of "42 °C ON"
and "46 °C OFF".
DHW loading with a gas fired boiler
The DHW heating will be activated if
the cylinder temperature falls 2.5 K
below the set cylinder temperature.
The burner, the circulation pump and
the three-way valve are started or
changed over. In the delivered condi-
tion, the set boiler temperature lies
20 K higher than the set cylinder tem-
perature (adjustable in coding
address 60). If the actual cylinder
temperature rises 2.5 K above the set
cylinder temperature, the burner will
be switched OFF and the cylinder
loading pump run-on time will be acti-
vated.