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Error code reference
Lennox Furnace Error Code LED1-ALT_FAST_FLASH/LED2-ALT_FAST_FLASH
Improper main ground or line voltage below 75 volts; OR broken ignitor; OR open ignitor circuit.
SourceLennox G27M Series Furnace - Service Manualp. 5
Diagnostic procedure
The full LED1-ALT_FAST_FLASH/LED2-ALT_FAST_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 the unit is properly grounded. Check line voltage is above 75V. Check ignitor resistance (10.9-19.7 ohms).
SourceLennox G27M Series Furnace - Service Manualp. 5
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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