Navien NCB-150E Service Manual page 103

Check method
Fault
Defective safety device
Temperature sensor error
Other potential issues
102 NCB-E Service Manual
Possible Causes
Check if the contact point of the overheat controller is defective.
Defective overheat
controller
Use a multi-meter to see if the resistance is normal (0.3Ω) or abnormal (∞).
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Check if the overheat controller wire is disconnected ( Normal resistance : 0.3Ω )
1. If the hot water temperature is sensed lower than it actually is due to a
defective sensor, check if the deviation of temperature is large due to a
Defective hot water defective temperature sensor.
output temperature
●
sensor
2. Measure the temperature sensor resistance, and determine if the sensor is
defective.
1. If the Max switch #1 of 1-1 is on,
Set the switch to the normal operation position.
Capacity setting
2. PCB DIP S / W capacity setting error can suddenly increase the hot water
temperature.(refer to page 18)
The surface temperature rises due to heavy scale deposits in the primary heat
Primary heat exchanger
exchanger.
overheated
Flush the primary heat exchanger.
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Defective PCB If the issue continues despite checking the items above, the PCB is defective.
Check method
Overheat controller
Check the output temperature displayed on the front panel.
Version 1.4