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240 (T-H3J), 340 (T-H3S) and 540 (T-H3) models Service Manial
Ver. 1.00
CONFIDENTIAL
10-14. Hi-limit switch
Part#
• 319143-228 (EM212)
240 (T-H3J) /340 (T-H3S) models
• 319143-095 (EKN34)
540 (T-H3) models
Unit Part#
#412
Function
-Based on bi-metal thermal expansion.
-Detects excessively high water temperature 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 "111" or
"121" 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) or 194 ˚F (90 ˚C).
Note: The outlet and heat exchanger thermistors 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 "111" or "121" error code will display.
Error codes when hi-limit
switch fails
111
121
The water heaters don't have the "141" error code that was used in our
previous models. This error code is now replaced by the "111" and the
"121" 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
Checkpoint
C1
When detecting temperature of the hi-limit switch exceeds the activation temperature
either 185 ˚F (85 ˚C) or 194 ˚F (90 ˚C), the reset button trips and switch goes to OFF mode.
Deactivation: to reset switch back to ON mode, press the reset button
US-603
K
8
5
5/8" (15 mm)
1-1/4" (33 mm)
"85" mark
A
A
H
S
I
240 (T-H3J) / 340 (T-H3S) models
540 (T-H3) models
Reset Button
Activation temp : < 185 ˚F (85 ˚C)
Activation temp : < 194 ˚F (90 ˚C)
1-1/4" (31 mm)
1-1/4" (31 mm)
5/8" (16 mm)
Reset Button