Takagi T-K3 Service Manual page 24

10-12. Hi-limit switch
T-K3 Part #
-Based on bi-metal thermal expansion.
-Detects excessively high water temperature (more than 194˚F or 90 ˚ C) in pipes of the
heat exchanger.
Function
-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".
Failure event 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).
Effects on the T-K3 Note: The mixing and outlet thermistors always act as backup hi-limit detectors to detect
if hi-limit switch fails.
2. The T-K3 is always shut down immediately after the ignition process, and either the
"111" or "121" error code will display.
Error codes when
The T-K3 doesn't have the "141" error code that was used in our previous models.
hi-limit switch fails.
This error code is now replaced by the "111" and the "121" error codes.
1. Visual inspection: connection/breakage of wires. Possibility also includes scale
deposits inside the heat exchanger.
Diagnostic
2. Check voltages and resistance: proper range of values shown below.
Color/Number of
Blue-Blue
wires
When temperatures exceed 194˚F (90˚C), the reset button trips and switch goes to OFF mode.
ON mode : <194˚F (90˚C)
#409 Takagi Part #
excessively high water temperatures in the heat exchanger.
111 121
Less than 1Ω
OFF mode : to reset switch back to ON mode, press the reset button
3/4 " ( 18. 4 mm)
EKN34 Checkpoint
Reset Button
24
CONFIDENTIAL
T-K3 Servi c e Manual
Ver. 1.05
C1
5/ 8" ( 15m m)