T-K3 Service Manual
Ver. 1.05
24
CONFIDENTIAL
10-12. Hi-limit switch
T-K3 Part #
#409
Takagi Part #
EKN34
Checkpoint
C1
Function
Failure event
Effects on the T-K3
if hi-limit switch fails.
111
121
Diagnostic
Color/Number of
wires
Blue-Blue
When temperatures exceed 194
˚
F (90
˚
C), the reset button trips and switch goes to OFF mode.
ON mode : <194
˚
F (90
˚
C)
OFF mode : to reset switch back to ON mode, press the reset button
Error codes when
hi-limit switch fails.
Less than 1
Ω
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.
-Based on bi-metal thermal expansion.
-Detects excessively high water temperature (more than 194
˚
F or 90
˚
C) in pipes of the
heat exchanger.
-After detection, communication between the computer board and gas valves are severed,
shutting down the T-K3 instantly. The "111" or "121" error codes will display.
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".
1. Unable to shut down the T-K3 if the water temperature from the heat exchanger
exceeds 194
˚
F (90
˚
C).
Note: The mixing and outlet thermistors always act as backup hi-limit detectors to detect
excessively high water temperatures in the heat exchanger.
2. The T-K3 is always shut down immediately after the ignition process, and either the
"111" or "121" error code will display.
The T-K3 doesn'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.
1-
3/8"
(35mm
)
5/ 8" ( 15m m)
3/4 " ( 18.4 mm)
Reset Button