LG GEN2 Series Installation And Operation Manual page 89

Troubleshooting - 4:1 or High Turndown Modulating Furnace
4:1 or High Turndown Modulating Furnace with Microprocessor Controller Will Not Light In all
cases, verify correct terminals as shown on the unit-specific wiring diagram.
...continued from previous page
Ignition Controller (IC#) red LED
blinks 1 time, 2 times or 4 times
or
Microprocessor Alarm: 'IG
furnace no flame after 3 trials'?
No
Flame lights but doesn't
travel all the way across
the burner manifold?
No
Flame flashes back
during light off?
No
Microprocessor Alarm:
'High temp. alarm - pressure fault
with excessive discharge temp.
Check for high limit trip.'?
No
Microprocessor Alarm:
'IG furnace max retry'?
No
Everything is working properly,
consult factory.
Manual supply gas valve off or combo valve (MV) switch turned off
Turn supply gas valve or combo valve on
Yes
Adjust inlet gas pressure to the range specified on the furnace label
(refer to 4:1 Electronic Modulation Start-Up section)
Faulty spark rod or spark gap does not equal 1/8 inch
Replace spark rod or adjust gap to 1/8 inch
Spark wire or connections faulty Repair
Flame sensor faulty, grounded, or faulty connection to
Replace or unground flame sensor or repair connection
Flame spread gap on outlet of burner pinched or blocked
Yes
One or more orifices fully or partially plugged
Yes
Inspect and replace heat exchanger if necessary
Combustion air inlet or discharge passageway restricted
Discharge temperature was above high limit control (HLC)
Yes
Pressure switch (PS2) trip due to high discharge temp
(Check pressure at combustion fan pressure tap with furnace running and
compare reading to pressure setting of pressure switches.)
1. If Pressure switch trips at wrong pressure, replace pressure switch.
2. If the combustion fan does not generate enough pressure,
Yes
Furnace has reached its maximum number of automatic error
1. Review alarm history and correct any issues identified
2. Reset the max retry alarm by pressing the alarm button on the
Microprocessor twice. Verify proper furnace operation.
Inlet gas pressure incorrect
Improper manifold pressure
Set high and low manifold pressure
connections or replace wire
flame sensor
Spread gap or remove debris
Inspect and clean or replace orifices
Heat exchanger cracked
Inspect and remove restriction
Wait for high limit to cool and reset
consult the factory.
resets