Viessmann VITOTRONIC 300 Installation And Service Instructions Manual page 21

External connections on plug aBÖ
¨ The external connections must be volt-free. Plug aBÖ must remain
plugged in, even if no connection is made.
A
A
B
C
External burner blocking
H
H
¨ Only safety shutdown
equipment, e.g. high limit
thermostats, may be connected
to these terminals. During this
shutdown, the heating system
is not protected against frost
and the boiler is not held at the
lower boiler water temperature.
C
D
B
D
E
F
External burner start
H
H
External safety equipment
H
H
Emergency mode
E
F
not
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