Navien NFC-175, Service Manual

Page: 85 / 138

NFC Service Manual 85 Version 1.0
Check method
Fault Possible Causes Check method
Defective safety device
Defective overheat
controller
Check if the contact point of the overheat controller is defective.
●
Use a multi-meter to see if the resistance is normal (0.3Ω) or abnormal (∞).
Overheat controller
Check if the overheat controller wire is disconnected ( Normal resistance : 0.3Ω )
Temperature sensor error
Defective hot water
output temperature
sensor
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 temperature sensor.
●
Check the output temperature displayed on the front panel.
2. Measure the temperature sensor resistance, and determine if the sensor is
defective.
Other potential issues
Capacity setting
1. If the Max switch #1 of 1-1 is on,
Set the switch to the normal operation position.
2. A PCB DIP S/W capacity setting error can suddenly increase the space heating
water temperature (refer to page 16).
Heat exchanger assembly
overheated
The surface temperature rises due to heavy scale deposits in the heat exchanger
assembly.
●
Flush the heat exchanger assembly.
Defective PCB If the issue continues despite checking the items above, the PCB is defective.