Error code reference

Lennox Furnace Error Code LED1 SLOW FLASH / LED2 OFF

Primary or secondary limit switch open. Limit must close within 3 minutes or unit goes into 1 hour Watchguard.

SourceLennox ML195UH Series - Service Manual: Gas Furnacep. 9

Diagnostic procedure

The full LED1 SLOW FLASH / LED2 OFF 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 for restricted airflow, dirty filter, or blower issues.

SourceLennox ML195UH Series - Service Manual: Gas Furnacep. 9

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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