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Error code reference
Lennox Furnace Error Code LED1 FAST FLASH / LED2 SLOW FLASH
Main power polarity reversed or improper main ground. Switch line and neutral.
SourceLennox G51MP Series Furnace - Service ManualPage 14, Table 8
Diagnostic procedure
The full LED1 FAST FLASH / LED2 SLOW FLASH procedure
Step 1 is visible so you can confirm you are on the right page. The remaining steps, the ones that tell you whether to actually replace a part, unlock with any pass.
MyPros+ · DiagnosticsStep 1 preview
1
First diagnostic step
Check that 120V has line and neutral correctly input into control; reverse line and neutral at 120V field connection.
SourceLennox G51MP Series Furnace - Service ManualPage 14, Table 8
More steps, wiring diagram references, and verified part numbers
Includes expected resistance and voltage values, connector pinouts, and supersession notes for replacement parts.
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Where this code is documented
18 manuals in the MyPros+ library document this code for Lennox furnace.
Models covered by the manuals that document this code
- 90UGFA2-50
- 90UGFA3-50
- 90UGFA3-75
- 90UGFA3/4-100
- 90UGFA4/5-125
- F8AUH**-24-045
- F8AUH**-24-045X
- F8AUH**-24-060
- F8AUH**-24-075
- F8AUH**-36-060
- F8AUH**-36-060X
- F8AUH**-36-075
- F8AUH**-36-075X
- F8AUHX
- G23Q2(X)-50
- G23Q2/3(X)-75
- G23Q3(X)-100
- G23Q3(X)-50
- G23Q3/4(X)-100
- G23Q3/4(X)-125
- G23Q4/5(X)-100
- G23Q4/5(X)-75
- G23Q5/6(X)-125
- G23Q5/6(X)-150
More models are covered than are listed here.
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