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Error code reference
Lennox Furnace Error Code LED1-ALT_SLOW_FLASH/LED2-ALT_SLOW_FLASH
Watchguard - burners fail to ignite.
SourceLennox G27M Series Furnace - Service Manualp. 5
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 that gas is being supplied to the unit. Check line pressure at the gas valve.
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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