T-M50 / T-M50 ASME Service manual
Ver. 1.05
25
CONFIDENTIAL
10-10. Thermistors
Unit Part #
#424 (Inlet)
#405 (Output)
#430 (Mixing)
AOS Part #
EKK38 (Inlet)
EKK2T (Output)
EKK1A (Mixing)
Checkpoint
E1 (Mixing)
E2 (Output)
E3 (Inlet)
Function
Measures cold / hot water temperatures in the water heater.
Failure event
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, 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.
Inlet Black(42)-Black
Output Black(12)-Black
Color/Number of wires
Mixing Black(113)-Black
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)
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
R
es
is
ita
nc
e
/ k
Ω
(Inlet thermistor)
(Mixing thermistor)
(Output thermistor)
Blue
Black
Black
Insulating
