32
Servicing should only be performed by a Quali
fi
ed Service Technician
FAULT
CAUSE
CORRECTIVE ACTION
Flame Fail: Ignition
The gas valve is shutoff.
The unit has failed to prove
main burner ignition after
four (4) attempts.
Exception: Models 500 -
800 will lock out after one
retry for ignition. It will
require a manual reset
before attempting to
fi
re
again.
• Check wiring harness connection at
the gas valve and at the main control
board.
• Inspect spark electrode and associated
wiring for damage and connection.
Refer to the Instruction Manual for
removal and cleaning procedures.
Replace if necessary.
• Check for proper electrical grounding
of the unit.
• Check incoming supply gas pressure.
Natural gas pressures should be
between 4 - 14 inches w.c. and LP gas
pressures should be between 8 - 14
inches w.c.
• Verify that the plastic hose from the
gas valve to the air inlet is connected
and is not damaged or restricted.
• Verify that the vent/air intake pipes are
correctly installed and that there are
no obstructions.
• Check for 24 VAC to the gas valve at
the 2-pin connection on the side of the
main control board during the ignition
attempt. If no voltage is present,
replace the main control board.
• If 24 VAC is present at the main control
board, check the wiring between the
main control board and the gas valve.
Replace the wiring if necessary.
• If 24 VAC is present, check the outlet of
the valve to ensure the valve is
fl
owing
gas. With a manometer connected to
the outlet tap of the gas valve, when
the unit is in the prepurge period,
there should be a negative pressure
present. When the valve is energized
a change in pressure should occur. If
the pressure change does not occur,
the gas valve is not opening. Replace
the gas valve.
• Inspect
fl
ame sensor and associated
wiring. Refer to the Instruction Manual
for removal and cleaning procedures.
Replace if necessary.
• Inspect the burner. Refer to the
Instruction Manual for removal and
cleaning procedures. Replace if
necessary.
• Replace the main control board.
Table 10. Troubleshooting Chart - Fault Messages Displayed on UIM (Continued.)
Tank Temperature
64°F
Operating Setpoint
185°F
S t a t u s : F l a m e F a i l : I g n i t i o n
HELP
RESET
A. O. Smith XP
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