Navien NHB-055, Service Manual

Page: 67 / 147

NHB Service Manual 67 Version 1.0
4.9.3 Thermistor
Part Check Point
Function Measure Hot water, Cold water, Space heating outlet and inlet temperatures in the boiler.
Failure Event Unable to properly measure water temperature within the boiler.
Effects
1. If any of the thermistors fail, an error code appears before starting operation.
2. If resistance values are off, the boiler will produce temperature fluctuations in hot water.
Error Code E047, E205, E218, E278, E279
Diagnostic
1. Visual inspection: Check wire connections are secure.
2. Check the resistance of the sensor (Stop operating and lower the temperature before
checking).
Testing/inspection
information
Resistance range : Please refer to the table below
Wire Color: BLUE-BLUE
Inlet, Outlet
Exhaust Limit Temperature Sensor
Wire Color: BLUE-BLUE
Check if the hot water temperature sensor is open (Error type : MΩ Open)
Temp(°F) Thermistor(kΩ) Exhaust Limit Temperature Sensor(kΩ)
32~40 17.9~25.4
113.6~180.7
40~50 14.5~20.3 89.2~139.5
50~60 11.4~16.4 67.5~108.5
60~70 9.4~12.8 51.5~81.1
70~80 7.5~10.4
41.5~61.3
80~90 6~8.2
32.2~48.9
90~100 5.1~6.6
26.3~37.6
100~110 4.1~5.7
20.83~30.4