123
5790 733 - 07
Vitocrossal 300 CA3 Series 2.5 to 6.0 Installation/Service
Boiler Water Temperature Control
Function Description
Brief description
H
The boiler water temperature is regulated by modulating
the burner.
H
The set boiler water temperature is determined from
the following coding:
– Set supply temperature of the heating circuits
connected to the control unit and the heating circuits
connected via the LON BUS
– External demand
– DHW temperature target
H
When the DHW tank is heated, the default set boiler
water temperature is 36°F (20 K) above the set DHW
temperature (adjustable via coding “60” in the
“DHW”
group).
Emissions test function
Enable the emissions test function on all control units.
The following functions are activated:
H
Burner start
H
Starting all pumps
Note:
Only the heating circuit pump is switched ON in
the case of boiler section 2/boiler section 3 control
(this can be achieved through the relay test function
of the lead boiler control).
H
Mixing valve remains set to control function
Function duration < 30 min:
The burner operates at 100% output until the
temperature limiter in the burner control unit switches
off. The burner then cycles, with 100% output, around
the value at the temperature limiter.
Function duration > 30 min (continuous):
Boiler water temperature at max. set value,
e.g. 194°F (90°C).
The burner is operated in modulating mode.
This prevents excessive cycling if emissions testing
is carried out over an extended period.
Cascade Control Unit
Brief description
The supply temperature is regulated by starting or
stopping the burners or by starting/stopping individual
burner stages.
H
Standalone control (see page 124)
H
Sequential control (see page 124)
H
Subject to system version, a difference is made
between the condensing strategy (see page 125)
and 2 conventional boiler strategies (see pages 126
and
127).
