Viessmann FB2B Installation And Service Instructions Manual page 116

Troubleshooting
Repairs
(cont.)
Checking the outside temperature sensor
200
100
80
60
40
20
10
8
6
-20 -10 0 10 20 30
Temperature in °C
116
1. Pull plug "X3" from the control unit.
X3
2. Test the resistance of the outside
temperature sensor across terminals
"X3.1" and "X3.2" on the disconnec-
ted plug and compare it with the
curve.
3. Where actual values deviate severely
from the curve values, disconnect the
wires at the sensor and repeat test on
the sensor itself.
4. Subject to result, replace the lead or
the outside temperature sensor.