Viessmann Vitodens 300, Service Instructions Manual

Page: 94 / 128

H Emissions test function
K Boiler water temperature
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 then transferred to the burner
control unit. From the set and actual
boiler water temperatures, the burner
control unit calculates the modulation
level and regulates the burner accord-
ingly. The burner control unit limits the
boiler water temperature: by the con-
trol thermostat to 74 °C, by the elec-
tronic temperature limiter to 81 °C.
The temperature limiter in the safety
chain locks out the burner control unit
at a boiler water temperature of 100
°C.
DHW heating
DHW heating will be activated if the
cylinder temperature falls 2.5 K below
the set cylinder temperature. The
burner and the cylinder primary pump
are switched ON. In the delivered con-
dition, the set boiler water tempera-
ture lies 20 K above the set cylinder
temperature. If the actual cylinder
temperature rises 2.5 K above the set
cylinder temperature, the burner will
be switched OFF and the cylinder pri-
mary pump run-on time will be acti-
vated.
DHW heating boost
The backup heating function is acti-
vated, if a switching period is selected
for the fourth time phase. This period
must lie outside the switching times
for standard DHW heating to enable
the control unit to recognise the sig-
nal. The set temperature value for
backup heating is adjustable in coding
address "58".
Constant temperature control unit
(cont.)
94
Function description
5692
569
GB