Viessmann VITODENS 300 Service Instructions Manual page 103

Extensions for external connections (accessory)
External extension H2
The external extension is connected
to the boiler control unit via the KM
BUS. The following functions can be
controlled or processed simulta-
neously via the extension:
sK
DHW circulation pump
fÖ
Power supply
Function description
(cont.)
aVD
&
External blocking
(terminals 2 - 3)
&
External demand
(terminals 1 - 2)
&
External changeover of the
operating mode (terminals 1 -
2)
The allocation of function
"External changeover of oper-
ating mode" is selected via
coding address 91.
aVG KM BUS
103