Viessmann VITOTRONIC 100 GC1B Installation And Service Instructions Manual page 70

Installation Sequence
Multi Boiler System – Connecting an External Control Unit
Legend
A Boiler blocking
B Start boiler as the last one in the boiler sequence
C External changeover of stepped/ modulating burners
70
Vitotronic 100, GC1B Installation and Service
Hooking Up On-site Control Devices Via LON
Boiler Blocking
Contact at terminals "1" and "2" of plug aVD:
Contact closed:
The boiler is blocked and has been removed from
the boiler sequence.
The isolation valve or the 3-way mixing valve for
constant return temperature raising, the shunt pump or
the boiler circuit pump are switched OFF.
The other boilers provide the required heating.
Note: If all boilers are blocked or there is no other boiler
ready for operation, then there will be no frost
protection for the heating system.
Contact open:
The boiler is reinstated into the current boiler sequence.
Start Boiler as the Last One in the Boiler Sequence
Contact at terminals "2" and "3" of plug aVD:
Contact closed:
The boiler is started as the last one in the boiler
sequence.
This boiler is started if the other boilers in the heating
system cannot provide sufficient heat.
Contact open:
The boiler is reinstated into the current boiler sequence.
(continued)