Viessmann VITOTRONIC 300 GW2 Installation And Service Instructions Manual page 28

Installation
Connection of the return temperature sensor
Strap-on temperature sensor and immersion temperature sensor
17A or 17B
740
720
700
680
660
640
620
600
580
560
540
20 30 40 50
68 86 104 122
Return temperature in
28
17A or 17B
60 70 70 80 90
140 158 176 194 212
°C / °F
100
For measuring the boiler return
temperature.
Electrical connection
The sensor is inserted in socket
"17A" or "17B" on the boiler
control.
Check the sensor
1. Disconnect plug aJA or aJB
in the terminal compartment of
the boiler control.
2. Measure resistance of sensor
at terminals "1" and "2" of the
plug.
Return Resistance
in 
temperature
in °C / °F
30 / 86 569
40 / 104 592
60 / 140 643
3. Compare the value measured
with the current temperature. If
the value differs significantly,
check installation and, if
necessary, replace sensor.
Technical data
Degree of protection: IP 32
Ambient temperature
During operation:
0 to + 100°C
32 to + 212°F
During storage and transport:
-20 to + 70°C
-4 to + 158°F