Navien NCB500-2S/37K Service Manual page 88

Check method
Fault
Defective sensor
Possible Issues
Possible Causes
Defective temperature Check if the temperature sensor is open and if the connector is connected
sensor connector properly.
Check the resistance of the temperature sensor. (Defective if it is 40kΩ or
higher)
Temperature sensor
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Defective PCB If the issues continue despite checking the items above, replace the PCB.
<DHW Flow sensor input temperature sensor / connector>
Check if the hot water temperature sensor is open (Error type: MΩ Open)
Replace the temperature sensor if the resistance value is abnormal.
Check the temperature displayed on the front panel.
Check method
Troubleshooting 87