520 Indoor / 520 Outdoor Service Manual
Ver. 1.00
33
CONFIDENTIAL
10-15. Hi-limit switch for exhaust
Unit Part #
#442
AOS Part #
319143-104
Checkpoint
K2
Function
-Based on bi-metal thermal expansion.
-Detects excess temperature (more than 151
˚
F or 66
˚
C) of exhaust gas in the
exhaust chamber.
Failure events
1. Unable to detect excess temperature of gas if switch fails "closed".
2. Continuous detection of excess temperatures (regardless of what the actual
temperature is) if switch fails "open".
Effects on the water
heater if hi-limit switch
for exhaust fails
1. Unable to shut down the water heater if the exhaust gas temperature in the
exhaust chamber exceeds 151
˚
F (66
˚
C).
2. The water heater is always shut down immediately after the ignition process,
and the "941" error code will display.
Error codes when hi-limit
switch
for
exhaust
fails
941 (520 Indoor only)
Diagnostic
1. Visual inspection: connection/breakage of wires.
2. Check voltages and resistance: proper range of values shown below.
Color/Number of wires
White - White
Less than 1.0
Ω
When temperatures exceed 151
˚
F (66
˚
C), the reset button trips and switch goes to OFF mode.
ON mode : <151
˚
F (66
˚
C)
OFF mode: automatic restoration back to ON mode
1
-
3
/
8
"
(
3
5
m
m
)
3/ 4 " (1 8 .4m m )
3 / 4 " ( 1 7 m m )
3 / 4 " ( 1 8 m m )
1
/
4
"
(
4
.
6
m
m
)
5
/
8
"
(
1
4
.
5
m
m
)
3 - 7 / 8 " ( 1 00 m m )
