Lennox Furnace Error Code E 274

E 274 is a soft lockout code indicating the furnace exceeded its maximum number of allowed restart attempts and the last attempt failed because the high-limit circuit opened or stayed open for more than 3 minutes. The limit circuit is a thermal protection system that shuts off the burner when the heat exchanger area overheats. This code points to an ongoing airflow restriction, incorrect firing rate, or a flue blockage that is preventing safe heat dissipation. The furnace enters a 1-hour soft lockout and will attempt to resume operation automatically after that period.

E 274 is a soft lockout, which means it clears automatically after approximately 1 hour and when the furnace successfully completes a heating call. A manual power reset may clear the displayed code temporarily, but if the underlying problem is not corrected, the furnace will recycle through failed attempts again and re-enter lockout. The code will clear reliably and stay clear only once the root cause of the repeated limit trips has been resolved.

If the fix is simply replacing an air filter or clearing a blocked vent, the cost is minimal, typically just a few dollars for a replacement filter. If a technician is needed to adjust the firing rate or inspect the system, a diagnostic service call generally runs between $75 and $150 depending on location. Replacing a faulty high-limit switch typically costs between $100 and $300 including parts and labor. More involved repairs such as a flue system correction or blower motor issues can range higher depending on the specific components involved.

Some of the common causes can be addressed by a homeowner, including replacing a dirty air filter, opening closed vents, and checking the exterior flue and combustion air pipes for visible obstructions. However, if the error persists after addressing those items, diagnosing the firing rate or testing the high-limit switch requires gas pressure tools and electrical testing equipment that are better suited to a qualified HVAC technician. Continuing to operate a furnace that is repeatedly overheating can cause long-term damage to the heat exchanger.

The furnace is designed to stop operating and lock out precisely because the overheating condition is unsafe for continued operation. Repeated high-limit trips can stress the heat exchanger over time and, in extreme cases, may be associated with cracked heat exchangers that allow combustion gases to enter the living space. It is best to address the cause of the lockout before relying on the furnace for continued heating, especially in cold weather where workarounds might lead to ignoring the problem.