Viessmann VITOTRONIC 300 GW2 Installation And Service Instructions Manual page 41

Connection of external controls (VD2/VD2A only)
Modulating boilers – operation with external modulation controller
1st stage burner fA from Vitotronic.
Plug lÖ from Vitotronic via
modulation controller (BAS).
On the bulding automation unit with
modulation controller set the
minimum temperatures 5°C / 9°F
above the minimum boiler water
temperature of the boiler.
(continued)
Boiler activation, isolation valve
open or closed
Connect dry contact at terminals
"2" and "3" of the plug aVH.
Contact closed:
First, the preheat function for follow-
up boilers is activated (coding
address "2b").
When the preheat function finishes,
the minimum temperature is
maintained for the boiler, and the
burner stages/modulation can be
switched externally.
The boiler water temperature is
limited by the preset maximum
boiler water temperature or via the
mechanical adjustable high limit.
The setpoint value is selected via
the coding address "9b".
Contact open:
The isolation valve is closed after
approx. 5 minutes (coding address
"2C").
External override of the burner
stages is not possible, and no
minimum temperature is maintained.
Switch on 1st stage burner (basic
load)
Connect dry contact at terminals "1"
and "2" of the plug aVD.
Contact closed:
The 1st stage burner is switched on.
The full load is only switched on to
maintain the minimum temperature
(not with Vitocrossal 300). The
boiler water temperature is limited
by the electronic maximum
temperature limit (coding address
"06") if this is set below the value
preset on the mechanical adjustable
high limit "R".
Contact open:
The 1st stage burner is switched
off.
Installation
41