31
Servicing should only be performed by a Quali
fi
ed Service Technician
FAULT
CAUSE
CORRECTIVE ACTION
Air PS/HEX Temp SW
Either the air pressure
switch contacts are open,
the O-temp heat exchanger
switch has opened or the
burner door temperature
switch has opened.
Warning: If the burner door
temperature switch trips,
the burner door and the
burner door temperature
switch will be extremely
HOT. Allow the unit to cool
before touching. Failure to
follow this warning could
result in severe personal
injury, death, or substantial
property damage.
APS:
• Check the wiring connections to
switch. Wires should be connected
to the common and normally closed
terminals.
• Air intake lengths exceed the
maximum allowed lengths.
• Check for obstruction or blockage
in the air intake pipes or at
terminations.
• Check reference hoses connected to
the air pressure switch for blockage
or obstruction.
• Inspect the burner. Refer to the
Instruction Manual for removal and
cleaning procedures. Replace if
necessary.
• Inspect the heat exchanger. Refer to
the Instruction Manual for removal
and cleaning procedures. Replace if
necessary.
• Faulty air pressure switch. Replace
switch.
O-TEMP HEX SWITCH: (Applies to 285-
800 Models Only)
• Inspect the back of the inner
combustion chamber at burner level
for refractory breakdown / missing.
Replace heat exchanger if refractory
is broken and unit has
fi
red.
• Check continuity across two
contacts. Wires should be connected
at both poles of the normally closed
switch.
• Faulty O-Temp HEX Switch. Replace
switch.
BURNER DOOR TEMPERATURE
SWITCH: (Applies to 285-800 Models
Only)
• The underlying cause of the fault must
be identi
fi
ed and resolved by a quali
fi
ed
service technician before resetting the
burner door temperature switch.
• Check continuity across two contacts.
Wires should be connected at both poles
of the normally closed switch.
• Faulty burner door temperature switch.
Replace burner door temperature
switch.
Table 10. Troubleshooting Chart - Fault Messages Displayed on UIM (Continued.)
Tank Temperature
73°F
Operating Setpoint
185°F
S t a t u s : A i r P S / H E X Te m p SW
HELP
RESET
A. O. Smith XP
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