Lennox SLP98UHV Error Code E 273: Soft Lockout - Flame Failure
What Does Code E 273 Mean?
The E 273 error code on the Lennox SLP98UHV indicates a soft lockout caused by repeated flame failures. The furnace successfully ignited but the flame kept going out during operation, and after exceeding the maximum number of retry attempts, the system locked itself out as a safety precaution.
The flame sensor is a thin metal rod positioned in the burner flame path. It works by conducting a tiny microamp-level electrical current through the flame. When the rod becomes coated with carbon deposits or oxidation over time, the current weakens until the control board can no longer reliably detect the flame. The board then shuts off the gas valve, thinking the flame has gone out.
This is one of the most common furnace issues and is usually resolved by cleaning the flame sensor. The lockout will clear automatically after a waiting period, or you can reset it by cycling power to the furnace after completing the repair.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Dirty flame sensor causing repeated flame signal loss | Most common | ✗ Call a pro → |
When to Call a Professional
Contact a licensed HVAC technician if:
- The flame sensor still causes lockouts after thorough cleaning
- The furnace ignites but the flame goes out within seconds repeatedly
- You notice the flame color is yellow or orange instead of blue
- The sensor rod is visibly pitted or corroded beyond what cleaning can fix
- The furnace displays other error codes alongside E 273
✓ Verified against manufacturer service manual — March 2026