A.O. Smith 110 Troubleshooting Manual - page 29
Troubleshooting Guide
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REPLACING THE HEAT EXCHANGER
There are many possible causes of a heat exchanger failure:
• Contaminated air with a high level of dust, lint, sand, grease, aerosols or other contaminants,
can become airborne and enter the air intake. The contaminants build up within the fan and
burner assembly causing abnormal flame conditions due to lack of combustion air, damaging
many components of the unit.
• Scale can build up from very hard water. Lime scale will form on the inside of the heat
exchanger tubes readily at high temperatures. This scale prohibits heat from reaching the water
which causes excessive heat within the heat exchanger copper, and it will eventually burn and
leak.
Along with changing the heat exchanger, it is important to identify the CAUSE of the need for
replacement, and fix the problem so it does not occur again
1) TOOLS ‐ Gather the following materials together:
a. Degreaser in a pump action bottle
b. Sheet of 100 Grit Sandpaper
c. #2 Philips Screw Driver
d. Needle‐Nosed Pliers
e. Duct Tape
f. Flashlight
g. Air Compressor
h. Old Towels, at Least Three
2) PREPARE THE UNIT
a. POWER ‐ Disconnect power to your unit.
b. GAS ‐ Shut off the gas supply to the unit.
c. WATER – Drain the unit. Refer to p. 21 for instructions.
3) REMOVE MANIFOLD/GAS ASSEMBLY, BURNER
a. Follow steps 1‐7 of the previous section, “Cleaning the Combustion Components”. This will tell
you how to remove the PCB, manifold/gas assembly, and burner
4) WIRES ‐ There are several wire clips that need to be removed to free the heat exchanger
a. Locate the brown wire clip connected to the GFI, and disconnect it.
b. On the bottom left, disconnect the ceramic heating elements (white wires).
c. Locate the white bypass valve clip on the left‐hand side of the combustion chamber with
red/black wires. Disconnect it.
d. Upwards toward the left side, remove a blue connection to the over‐heat cutoff fuse
e. Remove the two spade connections on the high limit switch.
f. Disconnect the igniter plug (purple wires and blue plug) at the bottom right.
g. Along the bottom, disconnect the plug into the proportional valve (red & white wires).