A.O. Smith T-D2-OS - Thermistors Specifications

T-D2-IN / T-D2-OS Service Manual
Ver. 1.00
27
CONFIDENTIAL
10-11. Thermistors
Unit Part #
#407 (Inlet)
#408 (Mixing)
#411 (Output)
Takagi Part #
EKK38 (Inlet)
EKK1A (Mixing)
EKK2T (Output)
Checkpoint
E1 (Mixing)
E2 (Output)
E3 (Inlet)
Function
Measures cold/hot water temperatures in the water heater.
Failure events
Unable to properly measure water temperatures within the water heater.
Effects on the water
heater if thermistor
fails
If the thermistors fail open or short, error code appears before starting operation.
If resistance values are just off, The water heater will have temperature fluctuations
in hot water.
Error codes when
thermistors fails
311 (Output) 321 (Inlet) 331 (Mixing)
Diagnostic
1. Visual inspection: connection/breakage of wires and/or debris on thermistor.
2. Check voltages and resistance; proper range of values shown below.
Color/Number of
wires
Inlet Black(42)-Black
68˚F (20°C) 9.0 to 13 kΩ
122˚F (50°C) 3.3 to 4.4 kΩ
176˚F (80°C) 1.4 to 1.8 kΩ
(see table below for more resistance values)
Output Black(12)-Black
Mixing Black(113)-Black
(Inlet thermistor) 42
(Output thermistor) 12
Resistance values of thermistors as a function of temperature
0.00
5.00
10.00
15.00
20.00
25.00
20 40 60 80 100 120 140 160 180 200 220
Temperature / ºF
Resisitance / kΩ
(Mixing thermistor) 113
Black
Blue
Black
Insulating