Viessmann VITOTRONIC 300 GW2 Installation And Service Instructions Manual page 43

Connection of external controls (CT3 only)
Vitocrossal 300 – operation with external modulation controller
1st stage burner fA from
Vitotronic 100.
Connection lÖ from Vitotronic has
no function.
Connection lÖ from building
automation system to the burner.
1st stage burner activated by the
modulation controller via connection
aVH.
(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 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 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
43