Viessmann VITOTRONIC 300 GW2 Installation And Service Instructions Manual page 35

Connections to terminal aBÖ (VD2/VD2A/CT3 only)
A Jumper
B External shut-off (dry contact)
Installation
External shut-off
1. Remove jumper between
terminals 16 and 17.
2. Connect dry contact.
Controlled switch-off takes
place when the contact is
opened.
WARNING
The terminals should be used for
safety switch-off purposes only
(e.g. through a high limit thermostat).
Start at page 52 for details of
controlled switch-off.
During switch-off, there is no frost
protection of the heating system
and the boiler is not kept at the
minimum boiler water temperature.
Emergency operation
Move jumper from terminals 16
and 17 to terminals 17 and 18.
35