Viessmann VITODENS 222-F Installation And Service Instructions Manual page 128

Function description
Weather-compensated control unit
Heating mode
The control unit determines a set boiler
water temperature subject to outside
temperature or room temperature (if a
room temperature-dependent remote
control is connected) and to the slope/
level of the heating curve.
The determined set boiler water temper-
ature is transferred to the burner control
unit. From the set and actual boiler water
temperatures, the burner control unit cal-
culates the modulation level and regu-
lates the burner accordingly.
Heating the DHW primary cylinder from cold
The heating circuit pump is switched ON
and the three-way diverter valve will be
changed over, if the cylinder tempera-
ture sensor captures a temperature
lower than the defaulted set tempera-
ture.
■ The cylinder primary pump is switched
ON if the boiler water temperature ≥
set DHW temperature.
■ The burner is switched ON if the boiler
water temperature ≤ set DHW temper-
ature, and the cylinder primary pump
is switched ON when the required
boiler water temperature is reached.
Boosting when DHW is drawn off
When DHW is drawn off, cold water
enters at the bottom of the primary cyl-
inder.
The heating circuit pump is switched ON
and the three-way diverter valve is
changed over, if the cylinder tempera-
ture sensor recognises a temperature
lower than the set temperature.
128
(cont.)
The electronic temperature limiter inside
the burner control unit limits the boiler
water temperature.
The primary cylinder is heated up to the
set DHW temperature. Heating stops
when the set temperatures have been
reached at the cylinder temperature sen-
sor and at the outlet temperature sen-
sor.
After heating, the cylinder primary pump
and the three-way diverter valve remain
ON for a further 30 s.
■ The cylinder primary pump is switched
ON if the boiler water temperature ≥
set DHW temperature.
■ The burner is switched ON if the boiler
water temperature ≤ set DHW temper-
ature, and the cylinder primary pump
is switched ON when the required
boiler water temperature is reached.