520 Indoor / 520 Outdoor Service Manual
Ver. 1.00
31
CONFIDENTIAL
10-13. Exhaust thermistor
Unit Part #
#706
AOS Part #
319143-131
Checkpoint
K1
Function
Measures the exhaust temperatures in the exhaust chamber.
Failure events
Unable to measure exhaust temperature in the exhaust chamber properly.
Effects on the water heater
if exhaust thermistor fails
If the thermistors fail open or short, error code appears before starting
operation. If resistance values are just off, the “341” error codes will
display.
Error codes when exhaust
thermistor fails
341 (520 Indoor only)
Diagnostic
1. Visual inspection: connection/breakage of wires and/or debris on
impeller.
2. Check voltages: proper range of values shown below.
Color/Number of wires
White - White
68
˚
F (20°C) 12.6 to 13.4 k
Ω
122
˚
F (50°C) 4.3 to 4.5 k
Ω
176
˚
F (80°C) 1.7 to 1.8 k
Ω
(see table below for more resistance values)
0.00
5.00
10.00
15.00
20.00
25.00
30.00
35.00
20
40
60
80
100
120
140
160
180
200
220
Tem perature / ºF
R
e
s
is
it
a
n
c
e
/
k
Ω
Resistance values of thermistors as a function of temperature
(Exhaust thermistor) 52
Black
Insulation
