LG GEN2 Series Installation And Operation Manual page 83

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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Supply air temperature above
Supply Temp Set Point?
No
Ignition Controller (IC#) red LED
blinks 7 times or is on?
No
120 VAC at 120/240 terminal on
Ignition Controller (IC#)?
Yes
Ignition Controller (IC#) red LED
blinks 6 times
or
Furnace Controller Alarm:
'Comb fan not proved'?
No
Furnace Controller Alarm:
'Low PSW with no call'?
No
Furnace Controller Alarm:
'High PSW with no call'?
No
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Wait for discharge temperature to cool or increase supply temp
Yes
setpoint sufficiently above inlet air temperature.
(Be sure to return this setting to the proper temperature
Faulty ground connection to ignition controller (IC#)
Yes
Incorrect voltage supplied to ignition controller Rewire
transformer or correct main voltage supply to unit (Voltage
No
Pressure switch tubing kinked, disconnected, plugged, or filled with
Yes
Straighten, connect, clear or replace pressure switch tubing
Combustion blower (CM) not functioning
Replace fusing (FU7), combustion blower(CM), or relay (IR)
Yes
Combustion blower operating with no call for heat to
Check wiring to combustion fan and correct as necessary
Ignition Controller (IC#) BLWR relay fault (relay stuck closed)
Repair or replace pressure switch (PS2)
Yes
Repair or replace pressure switch (PS5)
after testing furnace)
Repair or install proper ground
to controller must be 24-29 VAC)
Intermittent Controller Fault
Reset power to unit
Ignition Controller(s) (IC#) failed
Replace faulty ignition controller(s)
Fuse (FU8) Blown
Test and replace blown fuse
Furnace Transformer (TR5) fault
Replace heating transformer
water/ice.
Pressure switch (PS2) failure
Repair or replace pressure switch (PS2)
ignition controller
Replace ignition controller
Pressure switch (PS2) failure
Pressure switch (PS5) failure