Navien NCB-150E Service Manual page 105

Check method
Fault
Heat exchanger
overheated
Defective part
Other trouble
104 NCB-E Service Manual
Possible Causes
1. The error occurs due to high exhaust gas temperature caused by a damaged or
clogged heat exchanger.
Damaged or clogged
heat exchanger 2. Flush the heat exchanger to remove scale deposits.
3. Replace the heat exchanger if it is damaged or cannot be unclogged.
Defective contact point of the exhaust gas overheat controller 230°F (110°C) Max
Check connection of the overheat controller.
Defective overheat
●
controller
If the resistance is abnormal, replace the temperature sensor. (refer to page 66)
●
Check the output temperature displayed on the PCB.
●
Check if the heating water temperature sensor is open (Error type : MΩ Open)
Defective PCB If the issue continues despite checking the items above, replace the PCB.
Check method
Version 1.4