Lennox EL296UHV Error Code U: Discharge Air Temperature
What Does Code U Mean?
The letter "U" on the Lennox EL296UHV tells you the SureLight integrated control is reporting the discharge air temperature: the temperature of the conditioned air leaving the furnace. It is a diagnostic value the board tracks, and showing it lets an installer or technician read the supply temperature straight from the seven-segment display without a separate thermometer.
On a two-stage, variable-speed furnace this reading is especially useful because discharge temperature depends on which heating stage is firing and how much CFM the ECM blower is moving. Reading it during a heat call helps confirm the furnace is producing an appropriate temperature rise for the active stage and airflow.
"U" is one of several information readouts on this control, alongside "A" (blower CFM) and the mode letters such as "H", "h", and "C". It reports a measurement; it does not command any action and does not indicate a problem by itself.
What You'll Notice
- The display shows "U" followed by a temperature value while the furnace is running.
- The furnace continues normal operation; nothing shuts down when this reading appears.
How This Is Diagnosed
The "U" value simply reports the measured supply-air temperature, so reading it during a heat cycle is how you confirm the furnace is delivering a reasonable temperature rise. It would matter only if the discharge temperature reads implausibly low or high relative to the firing stage, which could hint at an airflow or sensor problem worth checking.
- The discharge temperature shown is unusually low during a high-fire heat call, suggesting airflow is too high or the burners are underperforming.
- The reading is extremely high, which can point to restricted airflow from a dirty filter or closed vents that should be corrected.
Frequently Asked Questions
What is the "U" reading on my Lennox furnace?
It is a diagnostic display of the discharge (supply) air temperature, meaning how warm the air leaving the furnace is. It is informational and not an error.
Do I need to do anything about the "U" value?
No. It is a measurement for reference. Only an unusually low or high reading, paired with poor heating, would suggest an airflow issue worth investigating.
✓ Verified against manufacturer service manual — March 2026