Navien NCB-150E Service Manual page 114

Check method
Fault
Defective temperature
Defective sensor
Temperature sensor
Defective circulation
Possible Issues
Possible Causes
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 30kΩ or higher)
Replace the temperature sensor if the resistance value is abnormal.
●
Check the temperature displayed on the front panel.
●
Check power supply to the circulation pump(AC 120V)
pump
Defective PCB If the issues continue despite checking the items above, replace the PCB.
<Heat exchanger output temperature sensor / connector>
<Check if the secondary water temperature sensor is open Error type : MΩ Open>
Check method
Troubleshooting 113