110 Indoor / 110 Outdoor Service Manual
Ver. 1.01
27
10-11. Hi-limit switch
Unit Part # #412 AOS Part # 319143-228
Checkpoint C1
Function
-Based on bi-metal thermal expansion.
-Detects excessively high water temperature (more than 185˚F or 85˚C) in pipes
of the heat exchanger.
-After detection, communication between the computer board and gas valves are
severed, shutting down the water heater instantly. The "11" or "12" error codes
will display.
Failure events
1. Unable to detect excessively high water temperatures if switch fails "closed".
2. Continuous detection of excessively high water temperatures (regardless of
what the actual water temperature is) if switch fails "open".
Effects on the water
heater if hi-limit switch
fails
1. Unable to shut down the water heater if the water temperature from the heat
exchanger exceeds 185˚F (85˚C).
Note: The outlet thermistor always act as backup hi-limit detectors to detect
excessively high water temperatures in the heat exchanger.
2. The water heater is always shut down immediately after the ignition process,
and either the "11" or "12" error code will display.
Error codes when hi-limit
switch fails
11 12
The 110 Indoor / 110 Outdoor don't have the "14" error code that was used in
our previous models. This error code is now replaced by the "11" and the "12"
error codes.
Diagnostic
1. Visual inspection: connection/breakage of wires. Possibility also includes
scale deposits inside the heat exchanger.
2. Check voltages and resistance: proper range of values shown below.
Color/Number of wires Blue-Blue
Less than 1.0 Ω
When temperatures exceed 185˚F (85˚C), the reset button trips and switch goes to OFF mode.
ON mode : <185˚F (85˚C) OFF mode: to reset switch back to ON mode, press the reset button
A
A HS I
US-603K
8 5
5/8" (14.9mm)1-1/4" (33mm)
"85" mark
Reset Button
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