T-H2-DV/T-H2-OS Service Manual
Ver. 1.01
35
CONFIDENTIAL
10-16. Overheat cutoff fuse
Unit Part #
#404
Takagi Part #
EX02A
Checkpoint
C2
Function
-The overheat cutoff fuse contains solder with a melting point of 430
˚
F
(221
˚
C).
-Detects excessive temperatures within the water heater, especially around
the heat exchanger and combustion chamber. Upon detection,
communication between the computer board and gas valves will sever,
shutting down the water heater instantly. The "111", "121" or “711”error
code will display.
Failure events
1. Unable to detect the excessively high temperatures within the water
heater.
Effects on the water
heater if the overheat
cutoff fuse fails
1. Flames from burner may penetrate a ruptured/damaged heat exchanger.
2. Gas valves will not operate.
Error codes when the
overheat cutoff fuse fails
111
121
711
Diagnostic
1. Visual inspection: connection/breakage of wires.
2. Check voltages and resistance: proper range of values shown below.
Color/Number of wires
Blue-Blue
Less than 1
Ω
Solder will melt at temperature exceeding 430
˚
F(±9
˚
F) or 221
˚
F (±5
˚
C)
2 9 - 1 / 2 " ( 7 5 0 m m )
The O.H.C.F. has a red line on itself.
