Thermistors - A.O. Smith 710 ASME Service Manual

10-10. Thermistors

Unit Part #
Function
Failure event
Effects on the water
heater if thermistor
fails
Error codes when
thermistors fails
Diagnostic
Color / Number of
wires
Resistance values of thermistors as a function of temperature
25.00
20.00
15.00
10.00
5.00
0.00
20
#422 (Inlet)
#433 (Output) AOS Part #
#418 (Mixing)
Measure cold / hot water temperatures in the water heater.
Unable to properly measure water temperatures within the water heater.
If the thermistors fail open or short, error code appears before starting operation.
If resistance values are just off, water heater will have temperature fluctuations in
hot water.
311 (Output)
1. Visual inspection: connection / breakage of wires and/or debris on thermistor.
2. Check voltages and resistance; proper range of values shown below.
Inlet Black (42)-Black
Output Black (12)-Black
Mixing Black (113)-Black
Insulating
40 60 80
319143-085 (Inlet)
319143-096 (Output)
319143-081 (Mixing)
321 (Inlet)
68˚F (20°C) 9.0 to 13 kΩ
122˚F (50°C) 3.3 to 4.4 kΩ
176˚F (50°C) 1.4 to 1.8 kΩ
(see table below for more resistance values)
Black
Blue
Black
100 120 140
Temperature / ºF
25
CONFIDENTIAL
710 / 710 ASME Service Manual
Checkpoint
331 (Mixing)
(Inlet thermistor) 42
(Mixing thermistor) 113
(Output thermistor) 12
160 180 200
Ver. 1.00
E1 (Mixing)
E2 (Output)
E3 (Inlet)
220