Viessmann Vitotronic 100 GC1 Installation And Service Instructions Manual page 23

Heating system designs
System version 6
(cont.)
Possible applications
The Vitocrossal 300 (lead boiler) and the Vitorond 200 (lag boiler) are operated via a Viessmann control system with outoor
reset logic, modulating boiler water temperature, and load-dependent sequential control – two-stage or modulating burners
are controlled.
Vitocrossal 300 is equipped with two return connections. The heating circuits with the higher return temperature are
connected to the upper return connection, and those with lower return temperatures to the lower return connection. Please
note: Connect at least 15% of the rated output to the lower return connection. The return temperature control is available
as accessory or must be provided on site.
Return temperature control for Vitorond can be achieved using the shunt pump and by closing the isolation valve.
Temperature sensor T1 controls the isolation valve. Temperature sensor T2 switches the shunt pump.
Due to the LON-BUS communication between controls, a boiler supply temperature is automatically set.
This temperature is based on the highest required mixing valve circuit temperature plus adjustable differential.
IMPORTANT
The connection diagram is only a recommendation and needs to be verified for completeness and functionality at the
installation site. Single-phase and three-phase pumps must be connected with field supplied motor contactors and/or motor
starters.
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