LG GEN2 Series Installation And Operation Manual page 84

Troubleshooting - 4:1 Modulating Furnace
4:1 Modulating Furnace with Stand-Alone Controller Will Not Light
In all cases, verify correct terminals as shown on the unit-specific wiring diagram.
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Furnace Controller Alarm:
'High Speed PSW Fault'?
No
24 VAC between 24 VAC
terminals on mod valve?
Yes
Does the 0-10 VDC signal at the
SIG+/- terminals on the mod
valve correspond to the heat %
shown on the controller?
Yes
Ignition Controller (IC#) red LED
blinks 1 time, 2 times or 4 times
or
Furnace Controller Alarm:
'No flame 3 trials'?
No
Flame lights but doesn't
travel all the way across
the burner manifold
No
Flame flashes back
during light off?
No
Continues on next page...
Pressure switch tubing kinked, disconnected, plugged, or
Straighten, connect, clear or replace pressure switch tubing
Yes
Combustion blower (CM) not functioning
Replace fusing (FU7), combustion blower or relay (CM)
No
Connection fault between terminal 20 and mod valve
Connection fault between pCOe and mod valve
No
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
Yes
Flame spread gap on outlet of burner pinched or blocked
One or more orifices fully or partially plugged
Yes
Inspect and replace heat exchanger if necessary
Combustion air inlet or discharge passageway restricted
filled with water/ice.
Pressure switch (PS5) failure
Repair or replace pressure switch (PS5)
Check and repair connection issue
Check and repair connection issue Furnace
controller defective
Replace defective parts
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