Lennox SLP98UHV Error Code E 274: Soft Lockout - Limit Circuit
What Does Code E 274 Mean?
Error code E274 on the Lennox SLP98UHV indicates a soft lockout after the limit circuit opened repeatedly or remained open for longer than 3 minutes. The furnace has shut down and will enter a 1-hour soft lockout before attempting to operate again.
This code is an escalation of E250 (limit switch open). While E250 is a single occurrence, E274 means the furnace recycled multiple times with the limit switch tripping each time, indicating a persistent overheating condition. The root cause must be addressed before the furnace can operate reliably.
The most common cause is a dirty air filter restricting airflow and causing the furnace to overheat repeatedly. Other causes include blocked or closed vents throughout the home, a failing blower motor, or ductwork restrictions.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Persistent airflow restriction causing repeated overheating | 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 and gas supply Turn off the furnace at the circuit breaker and turn the gas shutoff valve to the OFF position (handle perpendicular to the pipe). Allow the furnace to cool completely.
- Replace the air filter Locate and inspect the air filter. If it is dirty, replace it with a new filter of the correct size. Make sure the airflow arrow points toward the blower. If you recently upgraded to a higher-MERV filter, switch back to the manufacturer-recommended MERV rating.
- 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 unobstructed.
- Inspect accessible ductwork Check visible ductwork for collapsed flex duct, disconnected sections, or crushed portions that 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 1-hour lockout. Set your thermostat to call for heat and monitor through multiple heating cycles.
When to Call a Professional
Contact a licensed HVAC technician if:
- E274 or E250 returns after replacing the filter and opening all vents
- The blower motor sounds labored or is not running at full speed
- The limit switch trips within minutes of the furnace starting each time
- You also see E252 (discharge air temperature too high)
- The ductwork may be undersized for the furnace capacity
✓ Verified against manufacturer service manual — March 2026