Troubleshooting
8:1 Staged Furnace Will Not Light
24 VAC across R and X? | No |
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| Yes |
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| No |
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24 VAC across W1 and X? |
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| Yes |
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| No |
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24 VAC across 22 and 21? |
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Yes
N.O. contact on heat relay (RH) | No |
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closed? |
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| Yes |
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DT1 displayed on furnace | Yes |
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controller (SC1)? |
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| No |
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OT1 displayed on furnace | Yes |
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controller (SC1)? |
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| No |
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Blank screen on furnace | Yes |
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controller (SC1)? |
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| No |
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24 VAC across terminals | No |
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S and T? |
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| Yes |
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With the combustion blower | Yes |
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(CM) off, is the N.O. |
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airflow switch (PS2) closed? |
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| No |
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Continues on next page... |
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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 of 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 8:1 Staged
Furnace controller (SC1) defective
Replace furnace controller (SC1)
Airflow switch (PS2) defective
Replace defective airflow switch (PS2)
54 Model IG / IGX
®