Lennox Error Codes & Fault Codes
Complete LED flash code reference for Lennox furnaces. Bookmark this page for quick field lookups.
| Code | Description |
|---|---|
| Slow amber | Normal, no call for heat |
| Fast amber | Normal, call for heat active |
| Slow red | Ignition lockout |
| Fast red | Internal board fault |
| Red/Amber alt. | Reversed line voltage polarity |
| Red steady | High limit switch open |
| Amber steady | Pressure switch open |
| Both off | No power to unit |
Detailed Code Reference
Frequently Asked Questions
What does a slow red LED on a Lennox furnace mean?
A slow red flash on a Lennox furnace indicates an ignition lockout. The furnace attempted to ignite multiple times and failed. Common causes include a weak or failed hot surface igniter, low gas pressure, or a dirty flame sensor. Clean the flame sensor, check gas pressure, and power cycle to reset.
What does red and amber alternating mean on a Lennox furnace?
Red and amber LEDs alternating on a Lennox furnace means the line voltage polarity is reversed. The hot and neutral wires are swapped at the furnace junction box. Correct the wiring polarity to resolve this code.
How do I read Lennox furnace LED codes?
Lennox furnaces use a two-color LED system (red and amber). Amber indicates normal conditions: slow amber is standby, fast amber is active heating. Red indicates faults: slow red is ignition lockout, fast red is board fault, steady red is high limit open. Both LEDs off means no power to the unit.
Why is my Lennox furnace showing a steady amber light?
A steady amber light on a Lennox furnace indicates the pressure switch is open. This means the inducer motor is not creating enough draft, or the pressure switch itself has failed. Check the inducer motor, clear any flue obstructions, and test the pressure switch.
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