LG GEN2 Series Installation And Operation Manual page 88

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
120 VAC at 120/240 terminal on
Ignition Controller (IC#)?
Yes
Ignition Controller (IC#) red LED
blinks 6 times
or
Microprocessor Alarm:
'Combustion fan not proved'?
No
Microprocessor Alarm:
'Pressure Switch closed
with combustion fan off'?
No
Microprocessor Alarm:
'IG furnace high pressure'?
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
Continues on next page...
No
Pressure switch tubing kinked, disconnected,
Yes
Straighten, connect, clear or replace pressure switch tubing
Combustion blower (CM) not functioning
Replace fusing (FU7), combustion blower or relay (CM)
Combustion blower operating with no call for heat to
Check wiring to combustion fan and correct as necessary
Yes
Ignition Controller (IC#) BLWR relay fault (relay stuck closed)
Yes
Pressure switch tubing kinked, disconnected,
Straighten, connect, clear or replace pressure switch tubing
Combustion blower (CM) not functioning
No
Replace fusing (FU7), combustion blower or relay (CM)
Connection fault between terminal 20 and mod valve
No
Connection fault between pCOe and mod valve
Microprocessor controller or pCOe defective
Fuse (FU8) Blown
Test and replace blown fuse
Furnace Transformer (TR5) fault
Replace heating transformer
plugged, or filled with water/ice.
Pressure switch (PS2) failure
Repair or replace pressure switch (PS2)
ignition controller
Replace ignition controller
Pressure switch (PS2) failure
Repair or replace pressure switch (PS2)
plugged, or filled with water/ice.
Pressure switch (PS5) failure
Repair or replace pressure switch (PS5)
Check and repair connection issue
Check and repair connection issue
Replace defective parts