Viessmann Vitodens 300 Service Instructions Manual page 88

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. The lockout can be reset no sooner than after 20
minutes by pressing reset E.
Note
The equipment will also be locked out again for 20 minutes if the mains power
supply is switched OFF.
88
2. Check the sensor resistance and
compare actual values with the
curve.
3. Replace the sensor in case of
severe deviation.
Danger
The boiler temperature sen-
sor is immersed in the heat-
ing water (risk of scalding).
Drain the boiler before repla-
cing the sensor.