Lennox SLP98UHV Error Code Soft Lockout - Limit Circuit Recycle: Soft Lockout - Limit Circuit Recycle

What Does Code Soft Lockout - Limit Circuit Recycle Mean?

Error code E274 on the Lennox IFC control board indicates that the furnace has exceeded its maximum number of limit switch recycles and has entered a soft lockout. This code is the escalation of E250 (Limit Switch Circuit Open). Each time the furnace overheats and the limit switch trips, the board counts it as a recycle. Once the preset limit of consecutive recycles is exceeded, the board locks out with E274 to prevent further thermal stress.

This escalation means the overheating condition has been happening repeatedly — the furnace has been trying to run, overheating, shutting down, cooling off, and restarting multiple times. Each cycle puts stress on the heat exchanger, and prolonged overheating can eventually crack it, leading to an extremely expensive repair. So E274 is the board's way of saying "enough — something needs to change before I'll try again."

The root cause is the same as E250: restricted airflow across the heat exchanger. A dirty air filter is the most common culprit by far, followed by blocked or closed registers and a dirty blower wheel. Because this is a soft lockout, the furnace will attempt to restart after the lockout period, but it will immediately lock out again if the airflow restriction isn't resolved.

How to Fix It: Replace the Air Filter and Restore Airflow

What You'll Need

• New furnace air filter (correct size for your Lennox unit)
• Flashlight

Steps

1. Turn off power AND shut off gas supply Switch the furnace power off at the disconnect switch near the unit AND at the circuit breaker. Locate the gas shutoff valve on the gas line leading to the furnace and turn it to the OFF position (perpendicular to the pipe). If you smell gas at any point, leave the area immediately and call your gas company from outside.
2. Replace the air filter immediately Locate the air filter on your Lennox furnace — typically in the return air duct opening on the side or bottom of the cabinet. Remove the old filter, note the size, and install a new filter with the airflow direction arrow pointing toward the furnace (toward the blower). If you don't have a replacement filter available, at minimum remove the clogged filter temporarily so the furnace can breathe.
3. Open all supply and return vents throughout the home Walk through every room and ensure all supply registers and return air grilles are fully open and unobstructed. Move furniture, rugs, or curtains that may be blocking vents. At least 80% of registers must be open for proper airflow on Lennox systems.
4. Inspect the blower compartment With power still off, open the blower compartment door and check the blower wheel for heavy dust buildup. A caked blower wheel significantly reduces airflow. Vacuum any loose debris you can reach. If the wheel is heavily coated, note this for a professional cleaning.
5. Wait for the furnace to cool completely Because the furnace has been repeatedly overheating, let it sit with power off for at least 15–20 minutes to allow the heat exchanger and limit switch to fully cool down and reset.
6. Restore power and test Replace the access panel. Turn the gas supply back on (valve handle parallel to the pipe). Restore power at the disconnect switch and breaker. Cycling the power clears the soft lockout. Set your thermostat to call for heat and observe the furnace through an entire heating cycle.

When to Call a Professional

Contact a licensed HVAC technician if:

• The filter is new and vents are open but E274 or E250 continues to occur
• The blower motor is running but airflow from the supply registers is weak
• The blower motor makes grinding, squealing, or humming noises
• The blower wheel is heavily caked with debris and needs professional cleaning
• You notice a gas smell at any point during the process