Overheat Cutoff Fuse - A.O. Smith 710 ASME Service Manual

10-12. Overheat cutoff fuse

Unit Part #
Function
Failure event
Effects on the water
heater if the overheat
cutoff fuse fails
Error codes when
overheat cutoff fuse
fails
Diagnostic
Color / Number of wires
Solder will melt at temperature exceeding 430
#403 AOS Part #
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" or "121" error code
will display.
1. Unable to detect the excessively high temperatures within the water
heater.
1. Flames from burner may penetrate a ruptured/damaged heat exchanger.
2. Gas valves will not operate.
111
1. Visual inspection: connection / breakage of wires.
2. Check voltages and resistance: proper range of values shown below.
Blue-Blue Less than 1.0 Ω
710 / 710 ASME Service Manual
319143-286
˚F (±9˚F) / 221˚C (±5˚C)
3 1- 1 /2 " ( 80 0 mm )
27
CONFIDENTIAL
Ver. 1.00
Checkpoint C2
121