Viessmann VITODENS 300 Service Instructions Manual page 86

Troubleshooting
Repairs
(cont.)
Checking the flue gas temperature sensor
The flue gas temperature sensor locks out the boiler when the permissible flue
gas temperature is exceeded. Reset the interlock after the flue gas system has
cooled down by pressing the reset "E" button.
86
2. Check the sensor resistance and
compare the actual values with the
curve.
3. Replace the sensor in case of
severe deviation.
Danger
The boiler water tempera-
ture sensor is immersed in
the heating water (risk of
scalding).
Drain the boiler before repla-
cing the sensor.