Lennox EL296UHV Error Code E 252: Discharge Air Temperature Too High
What Does Code E 252 Mean?
Error code E 252 on the Lennox EL296UHV means the discharge air temperature — the temperature of the heated air leaving the furnace — climbed above its normal range during a gas heating call. This code is gas-heat only. The SureLight integrated control watches the supply-air temperature directly through its discharge sensor rather than waiting for the mechanical limit switch to trip, so E 252 is an early temperature warning.
Because the control is reading the actual air temperature, E 252 often shows up before the high-limit switch opens. Think of it as the step before E250: E 252 says the air is running hot, and if the restriction gets worse and the limit finally trips, you would then see E250, and a repeated trip escalates to the E274 one-hour lockout. E 252 clears on its own once the current heat call finishes, so it can appear and disappear between cycles while the underlying airflow problem is still present.
The usual reason the discharge air runs hot is that too little air is moving across the heat exchanger. When airflow is low, the same burner heat is dumped into a smaller volume of air, so that air leaves hotter. A clogged air filter is the most common culprit, followed by closed or blocked supply registers and return grilles, or too few open vents for the furnace's output. On this two-stage furnace, high fire is where the discharge temperature climbs fastest, so E 252 tends to appear on high heat first.
Other causes are technician territory: an over-fired gas input rate delivering more heat than the airflow can carry, or insufficient return-air ducting. This code is part of the same restricted-airflow family as E250, E311, and the discharge-temperature indications reported through the E310 discharge sensor and the control's "U" discharge-temp display. Because they share a root cause, clearing an airflow restriction often silences several of these at once.
What You'll Notice
- The seven-segment LED on the SureLight control shows E then 252
- Air at the supply registers feels noticeably hotter than usual
- The code appears during a heating call and clears once the call ends
- Airflow feels weak even though the burners are firing, especially on high heat
- The filter looks dirty, or several registers around the house are closed
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 at FiltersFast · 🛒 Find at Amazon
- Flashlight
Steps
- Turn off electrical power at the breaker and shut off the gas supply valve Flip the furnace circuit breaker (or service switch) to OFF, then turn the gas shutoff valve to the OFF position, with the handle perpendicular to the pipe. If you smell gas, leave immediately and call your gas company.
- Replace the air filter Pull the filter from the blower compartment or return duct. If it is dirty or you cannot see light through it, replace it. Install a new filter of the same size with the airflow arrow pointing toward the blower. If you upgraded to a dense high-MERV filter, consider returning to the recommended rating, since the added resistance drives discharge temperatures up.
- Open every supply register and return grille Go room to room and make sure all supply registers and return-air grilles are fully open and clear of furniture, rugs, and curtains. The more open the vents, the more air carries heat away and the lower the discharge temperature.
- Visually check accessible ductwork Where ducts are visible in the basement, attic, or crawl space, look for a crushed or collapsed flex duct or a disconnected joint. Only inspect what is safely reachable — do not open the blower housing or sealed duct.
- Restore gas and power, then test Turn the gas valve back to ON, with the handle parallel to the pipe, and flip the breaker back ON. Set the thermostat to call for heat. E 252 clears once a heating call finishes successfully, so run a full cycle and watch for it to return.
When to Call a Professional
Contact a licensed HVAC technician if:
- E 252 persists after the filter is replaced and all vents are open
- The supply air still feels extremely hot with a clean filter
- E250 or E274 appear alongside E 252
- The furnace was recently serviced or had gas work done and may be over-fired
- The return-air ducting or overall duct system looks undersized for the furnace
Frequently Asked Questions
Is E 252 a shutdown code?
Not by itself. E 252 is a discharge-temperature warning that clears when the heat call finishes. If the airflow restriction worsens and the high-limit trips, you would then see the E250 shutdown, and a repeated trip escalates to the E274 lockout.
The code cleared on its own — is the problem gone?
Not necessarily. E 252 always clears at the end of a heating call, so it can vanish while the restriction is still there. If the filter was dirty or vents were closed, fix that or the code will return on the next hot cycle.
Why does the air feel so hot with E 252?
Low airflow means the same burner heat is packed into less air, so the air leaving the furnace is hotter. Restoring full airflow spreads that heat over more air and brings the discharge temperature back to normal.
Could a closed vent in one room really cause this?
Several closed or blocked vents together can, because they reduce the total airflow the furnace can move. Opening all registers and return grilles is one of the simplest ways to lower the discharge temperature.
Sources
✓ Verified against manufacturer service manual — March 2026