mypros+
Error code reference

Lennox Furnace Error Code LED1 ALT FAST FLASH / LED2 ALT FAST FLASH

During ignitor warm-up: improper main ground, broken ignitor or open ignitor circuit, or line voltage below 75 volts. At power-up: circuit board failure or control wired incorrectly.

SourceLennox G50DF(X) Furnace - Full Service Manualp. 10

Lennox codesLennox furnace codes
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 ignitor resistance (10.9-19.7 ohms); check main ground; check line voltage above 75V.

SourceLennox G50DF(X) Furnace - Full Service Manualp. 10

Unlock with pass
Unlock with pass
Unlock with pass
More steps, wiring diagram references, and verified part numbers
Includes expected resistance and voltage values, connector pinouts, and supersession notes for replacement parts.
Unlock LED1 ALT FAST FLASH / LED2 ALT FAST FLASH procedure $9.95

Or subscribe: $29/month for all codes plus Max diagnostics, with 70 Max messages a day. Plus applicable tax.

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

Related Lennox furnace error codes

All Lennox furnace codes

75,000+ service documents · 20,000+ error codes · 100+ brands

Get Started

$29/month · Cancel anytime · Or $9.95 3-day pass · Plus applicable tax