Lennox EL296UHV Error Code E 250: Limit Switch Circuit Open
What Does Code E 250 Mean?
Error code E 250 on the Lennox EL296UHV means the high-limit switch circuit has opened. The high-limit is a safety switch that shuts off the gas burners the moment the air temperature inside the furnace climbs past a safe threshold. Its whole job is to protect the heat exchanger from overheating, which left unchecked could crack the exchanger or create a fire hazard.
When the limit opens, the SureLight integrated control cuts the burners but keeps the variable-speed ECM blower running to pull heat out of the exchanger and let the switch cool back down. If the limit closes again quickly, the furnace resumes normal operation. If it does not close within 3 minutes, the control escalates the situation into a one-hour soft lockout, which this board reports as its own code, E274. So E 250 is the first-level warning, and E274 is what you see if the overheating keeps happening.
Almost every E 250 traces back to insufficient airflow across the heat exchanger. When too little air moves through the furnace, the burners keep heating a small volume of air until it exceeds the limit's trip point. A dirty, clogged air filter is the single most common reason, followed by closed or blocked supply registers and return grilles. Because this is a two-stage furnace, an E 250 that appears mainly on high fire is a classic sign of an airflow restriction the system can tolerate on low heat but not on high.
Less common causes are not homeowner fixes: a weak or failing ECM blower motor, a collapsed or crushed duct, an over-fired gas input rate, or a limit switch that is failing on its own. These belong to a technician. The airflow codes on this board — E250, E252, E274, E291, and the E311 cutback warning — all point back to the same restricted-airflow family, so clearing the restriction usually resolves several of them at once.
What You'll Notice
- The seven-segment LED on the SureLight control shows E then 250
- The burners light but shut off early, while the blower keeps running to cool the furnace down
- The house is not reaching the thermostat setpoint even though the furnace is trying to run
- Airflow at the supply registers feels weak, and the air that does come out feels very hot
- The problem shows up more on high heat than on low, or the filter is visibly gray and clogged
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Dirty air filter restricting airflow | 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 the 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 Find the filter in the blower compartment or the return-air duct and pull it out. If it is gray, matted, or you cannot see light through it, it is almost certainly the cause. Install a new filter of the exact same size with the airflow arrow pointing toward the blower. If you recently switched to a thick high-MERV filter, go back to the MERV rating the furnace was set up for, because the denser media adds airflow resistance the high-limit can feel.
- Open every supply register and return grille Walk the whole house and make sure all supply registers and return-air grilles are fully open and clear of rugs, furniture, and curtains. Closing off rooms to save energy starves the furnace of return air and is a frequent hidden cause of limit trips.
- Visually check accessible ductwork Where you can see ducts in the basement, attic, or crawl space, look for a collapsed flex duct, a crushed section, or a disconnected joint restricting airflow. Only inspect what you can reach safely — do not open sealed duct or the blower housing.
- 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. Cycling power also resets any lockout timer. Set the thermostat to call for heat and watch the furnace through a full cycle, including high fire.
When to Call a Professional
Contact a licensed HVAC technician if:
- E 250 returns after the filter is replaced and all vents are open
- The blower motor is not running, runs slowly, or sounds labored during operation
- The high-limit trips within the first few minutes of the furnace starting
- E252, E274, or E291 appear alongside E 250
- The duct system looks undersized or was recently modified
Frequently Asked Questions
Why does E 250 keep coming back on high heat but not low?
On this two-stage furnace, high fire produces more heat and needs more airflow to carry it away. A restriction the system tolerates on low heat can still overheat the exchanger on high, tripping the limit and logging E 250.
Is it safe to keep running the furnace with E 250 showing?
The limit switch is doing its job by shutting the burners off, so it is protecting the furnace. But you should fix the airflow restriction promptly rather than repeatedly restarting it, because continued overheating stresses the heat exchanger.
What is the difference between E 250 and E274?
E 250 is a single limit-circuit-open event. If the limit keeps tripping or stays open longer than about 3 minutes, the control escalates to E274, a one-hour soft lockout. They share the same underlying airflow cause.
How often should I change the filter to avoid this?
It varies with filter type, pets, and dust levels in your home, so check it monthly and replace it whenever it looks dirty rather than following a fixed schedule.
Sources
✓ Verified against manufacturer service manual — March 2026