Viessmann VITODENS 242-F Installation And Service Instructions Manual page 145

Repair
(cont.)
6. Check the connections on the heat-
ing water and DHW side for contam-
ination and scaling; if required,
replace the plate heat exchanger.
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 system has cooled
down by pressing reset button R.
Fault "A3" during commissioning
During commissioning, the control unit
checks whether the flue gas temperature
sensor is correctly positioned.
If the flue gas temperature sensor is not
positioned correctly, commissioning is
cancelled and fault message A3 is dis-
played.
7. Install in reverse order using new
gaskets.
20
10
8
6
4
2
1
0.8
0.6
0.4
10 30 50 70 90 110
Temperature in °C
Sensor type: NTC 10 kΩ
1. Pull leads from flue gas temperature
sensor A.
2. Check the sensor resistance and
compare it with the curve.
3. In the case of severe deviation,
replace the sensor.
1. Check whether the flue gas temper-
ature sensor is correctly inserted.
See previous diagram.
Troubleshooting
145