Navien NCB-700-2S+/42K Service Manual page 92

Testing method
Fault
Defective sensor
Possible Issues
Possible causes
Temperature sensor Check if the temperature sensor is open and if the connector is connected
connection fault properly.
Check the resistance of the temperature sensor. The sensor is faulty if the
resistance is 30 kΩ or higher.
Temperature sensor fault
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PCB fault If the error condition continues after checking these items, replace the PCB.
<Heat exchanger input temperature sensor / connector>
Test to confirm if the hot water temperature sensor is open. Error: MΩ open circuit.
Testing method
Replace the temperature sensor if the resistance value is abnormal.
Check the temperature displayed on the front panel.
Troubleshooting 91