Troubleshooting
4:1 Modulating Furnace Will Not Light
24 VAC across R and X?
Yes
24 VAC across W1 and X?
Yes
24 VAC across 22 and 21?
Yes
N.O. contact on
heat relay (RH) closed?
Yes
DT1 displayed
on furnace controller (SC1)?
No
OT1 displayed
on furnace controller (SC1)?
No
Blank screen
on furnace controller (SC1)?
No
24 VAC across
terminals S and T?
Yes
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No
No
No
No
Yes
Yes
Yes
No
Main disconnect (DS1) open or defective
Close, repair or replace
Main transformer (TR1) fault
Replace main transformer
Heat switch (S4) open or not wired
Close or replace heat switch (S4)
Heat transformer (TR2) fault
Replace heating transformer
Heat relay (RH) is not energized
Check for loose connections. Repair or replace heat relay (RH)
Discharge air sensor (TS2) not wired or defective
Wire or replace discharge air sensor (TS2)
Outdoor air sensor (TS1) not wired or defective
Wire or replace outdoor temperature sensor (TS1)
Furnace controller (SC1) defective or not powered
Replace or wire furnace controller (SC1)
Discharge temperature was above high limit control (HLC1)
Wait for high limit to cool and reset
Inlet air sensor contact open
Adjust inlet air sensor setting (refer to 4:1 Modulation
Furnace controller (SC1) defective
Replace furnace controller (SC1)
52 Model IG / IGX
®
