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Error code reference
Lennox Furnace Error Code LED1 ALT SLOW FLASH / LED2 ALT SLOW FLASH
Watchguard: burners failed to ignite, or limit open more than 3 minutes, or lost flame sense 5 times in one heating cycle.
SourceLennox G50DF(X) Furnace - Full Service Manualp. 10
Diagnostic procedure
The full LED1 ALT SLOW FLASH / LED2 ALT 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 gas supply, gas valve wiring, ignitor, flame sensor.
SourceLennox G50DF(X) Furnace - Full Service Manualp. 10
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
2 manuals in the MyPros+ library document this code for Lennox furnace.
Models covered by the manuals that document this code
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