Viessmann Vitodens 333 Service Instructions Manual page 93

Weather compensated control unit
Heating mode
The control unit determines a set boil-
er water temperature subject to the
outside temperature or room tempera-
ture (if a room temperature dependent
remote control is connected) and the
slope/level of the heating curve. The
determined set boiler water tempera-
ture is transferred to the burner con-
trol unit.
From the set and actual boiler water
temperatures, the burner control unit
calculates the modulation level and
regulates the burner accordingly.
Heating the DHW storage cylinder from cold
The heating circuit pump is switched
ON and the three way diverter valve
will be changed over, if the cylinder
primary temperature sensor captures
a temperature lower than the set tem-
perature.
The cylinder primary pump will be
switched ON at a boiler water tem-
perature set DHW temperature.
At a boiler water temperature
DHW temperature, the burner will
be switched ON and, after the
required boiler water temperature
has been reached, the cylinder pri-
mary pump will be switched ON.
Boosting when DHW is drawn off
When DHW is drawn off, cold water
enters at the bottom of the cylinder.
(cont.)
The boiler water temperature will be
limited:
to 74 °C by the temperature control-
ler inside the burner control unit.
to 82 °C by the electronic tempera-
ture limiter inside the burner control
unit (during DHW heating to 87 °C).
to 100°C by the temperature limiter
in the safety chain (interlocks the
burner control unit).
The cylinder is then heated up to the
set DHW temperature. Heating stops
when the set temperature has been
reached at the cylinder primary tem-
perature sensor and at the outlet tem-
perature sensor.
After heating, the cylinder primary
pump and the three way diverter
valve remain ON for a further 30 s.
set
Function description
93