Lennox EL296UHV Error Code E 250: Limit Switch Circuit Open
What Does Code E 250 Mean?
Error code E250 on the Lennox EL296UHV indicates that the limit switch circuit is open. The limit switch is a safety device that shuts down the burners when the furnace's internal temperature exceeds a safe threshold. This prevents the heat exchanger from overheating, which could crack it or create a fire hazard.
When the limit switch opens, the burners turn off but the blower continues running to cool the heat exchanger. If the limit switch does not close within 3 minutes, the furnace enters a 1-hour soft lockout. Normal operation resumes after the fault is cleared.
The most common cause is a dirty air filter restricting airflow across the heat exchanger. When insufficient air passes over the exchanger, heat builds up until the limit switch trips. Other possible causes include blocked supply or return vents, an incorrect gas firing rate, or a blockage inside the heater. Less common causes include a failing blower motor or an undersized duct system.
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 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 Locate the air filter in the blower compartment or return air duct. Remove the old filter and check its condition — if it is visibly dirty or clogged, it is likely the cause. Install a new filter of the correct size with the airflow direction arrow pointing toward the blower. If you recently upgraded to a higher-MERV filter, consider going back to the originally recommended MERV rating, as higher ratings create more air resistance.
- Open all supply registers and return grilles Walk through every room and make sure all supply registers and return air grilles are fully open and not blocked by furniture, rugs, curtains, or other objects. Even partially closed vents reduce the total airflow the system can handle.
- Inspect accessible ductwork If you can see your ductwork in the basement, attic, or crawl space, check for collapsed flex duct, disconnected sections, or crushed portions that would restrict airflow.
- Restore power and gas, then test Turn the gas supply valve to ON (handle parallel to the pipe) and flip the circuit breaker to ON. Cycling the power resets the lockout. Set your thermostat to call for heat and monitor the furnace through a complete heating cycle.
When to Call a Professional
Contact a licensed HVAC technician if:
- E250 returns after replacing the filter and opening all vents
- The blower motor sounds labored or is not spinning at full speed
- The limit switch trips within minutes of the furnace starting
- You also see E274 (soft lockout from repeated limit trips)
- The duct system may be undersized for the furnace capacity
✓ Verified against manufacturer service manual — March 2026