Error code reference

Lennox Furnace Error Code LED1 SLOW FLASH / LED2 FAST FLASH

Low flame signal. Measures below 0.18 microamps (32M88) or 1.5 microamps (78M47/100973-01). Replace flame sense rod.

SourceLennox G43UF Series Furnace - Full Service Manualp. 11

Diagnostic procedure

The full LED1 SLOW FLASH / LED2 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 sensor rod for proper location and contamination. Clean with steel wool or replace sensor.

SourceLennox G43UF Series Furnace - Full Service Manualp. 11

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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