Heat Exchanger - A.O. Smith Water Heater 520 Direct Vent Indoor Service Manual

10-8. Heat exchanger

Unit Part #
Function
Failure events
Effects on the water
heater if the heat
exchanger fails
Error codes when the
heat exchanger fails
Diagnostic
Color/Number of wires
The heat exchanger of the 520 Indoor and 520 Outdoor has the "Pro" mark as shown below.
520 Indoor
#401
AOS Part #
#456
Absorbs heat from combustion and transfer it to water through the heat
exchanger pipes.
1. Clogged heat exchanger fins and/or cracks on the heat exchanger walls.
2. Leaking exhaust gas.
3. Improper heat transfer can cause the water in heat exchanger to boil.
1. Water leakage from the heat exchanger
2. Exhaust gas leakage (if this occurs, an overheat cutoff fuse is in place to
detect this event and immediately stop the water heater from operating)
3. Abnormal sounds during combustion
1. Visual inspection: soot deposits, cracks on the heat exchanger walls, and/or
water leakage from the heat exchanger.
2. In the event of abnormal sounds during combustion:
A. Inspect for soot buildup inside the heat exchanger.
B. Inspect for scale buildup inside the heat exchanger pipes. Scale
buildup obstructs proper heat transfer to the water, thereby overheating the
heat exchanger and causing damage.
520 Indoor / 520 Outdoor Service Manual
319143-064 (520 Indoor)
319143-118 (520 Outdoor)
N/A
N/A
520 Outdoor
25
CONFIDENTIAL
Ver. 1.00
Checkpoint N/A