Navien NHB-055 Service Manual page 108

Check method
Fault
Defective sensor
Possible Issues
108 NHB Service Manual
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 30kΩ or higher)
Temperature sensor
Replace the temperature sensor if the resistance value is abnormal.
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Check the temperature displayed on the front panel.
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Defective circulation
Check power supply to the circulation pump(AC 120V)
pump(external)
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
Version 1.0