Lennox EL296UHV Error Code E 252: Discharge Air Temperature Too High
What Does Code E 252 Mean?
Error code E252 on the Lennox EL296UHV indicates that the discharge air temperature is too high during gas heating. The control board monitors the temperature of the air leaving the furnace and generates this alert when it exceeds the safe operating range.
This is closely related to E250 (limit switch open) but E252 specifically measures the actual air temperature rather than relying solely on the mechanical limit switch. The EL296UHV's integrated control can detect elevated discharge temperatures before they reach the point where the limit switch trips, providing an early warning.
The most common cause is restricted airflow from a dirty air filter. When the filter is clogged, air moves too slowly across the heat exchanger, absorbing too much heat and exiting at an elevated temperature. The alert clears automatically when the current heating call finishes. Other causes include blocked or closed vents, an incorrect gas input rate (over-fired furnace), or insufficient return air. If not corrected, E252 can lead to E250 or E274 as the overheating worsens.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Restricted airflow from dirty filter | Most common | ✓ DIY fix → |
How to Fix It: Replace the Air Filter and Restore Airflow
What You'll Need
- Replacement air filter (matching size) Find on Amazon
- Flashlight
Steps
- Turn off electrical power at the breaker and shut off the gas supply valve Locate the furnace circuit breaker and flip it to OFF. Turn the gas shutoff valve to the OFF position (handle perpendicular to the pipe). If you smell gas, leave immediately and call your gas company.
- Replace the air filter Remove the current air filter from the blower compartment or return duct. If it looks dirty or you cannot see light through it when held up, it needs replacing. Install a new filter of the same size with the airflow arrow pointing toward the blower.
- Open all supply registers and return grilles Check every room in the house. Ensure all supply registers and return air grilles are fully open and not obstructed by furniture, rugs, or curtains. Restricted airflow anywhere in the duct system contributes to elevated discharge temperatures.
- Check the temperature rise After restoring power (next step), you can hold your hand near a supply register. The air should feel warm but not uncomfortably hot. If air feels extremely hot compared to normal, the airflow restriction may still be present.
- Restore power and gas, then test Turn the gas supply valve to ON and flip the circuit breaker to ON. Set your thermostat to call for heat. The E252 code clears after the heating call finishes successfully.
When to Call a Professional
Contact a licensed HVAC technician if:
- E252 persists after replacing the filter and opening all vents
- Discharge air feels extremely hot even with a clean filter
- You also see E250 or E274 codes alongside E252
- The furnace was recently serviced or had gas work done (possible over-firing)
- You suspect the duct system is undersized for the furnace
✓ Verified against manufacturer service manual — March 2026