Lennox 18J28 Limit Switch

When you're troubleshooting a furnace that's short-cycling or a blower motor that won't quit, the Lennox 18J28 Limit Switch is a primary diagnostic point. This genuine OEM furnace high limit switch is a critical safety component designed to monitor heat exchanger temperatures and prevent hazardous overheating. Featuring a 165F-CO (Cut-Out) and 135F-CI (Cut-In) thermal profile, this auto reset limit switch ensures the burner circuit opens if internal temperatures hit the 165°F threshold, only closing once the system cools to 135°F. This 7-inch insertion limit is a direct replacement for the Lennox 18J2801 and is compatible with a wide range of Lennox G23, G24, and LF24 series units. Whether you're dealing with restricted airflow from a clogged filter or a failing inducer, installing this OEM Lennox replacement part restores the precise thermal regulation required for safe, continuous operation in residential and commercial air handlers.

Key Benefits

• Direct Compatibility: Engineered as an exact functional equivalent to 18J2801 for seamless field installation.
• Automatic Reset: Eliminates the need for manual intervention by automatically resetting the circuit once temperatures return to safe operating levels.
• Extended Probe Length: The 7-inch sensing element provides accurate core temperature readings within the plenum or heat exchanger.
• Critical Safety Protection: Protects the heat exchanger from structural damage and prevents fire hazards by interrupting the gas valve circuit during overheat events.

Common Questions

What causes a Lennox 18J28 limit switch to trip repeatedly?
Frequent tripping, or short-cycling, usually points to airflow obstructions. Check for a dirty air filter, blocked return grilles, or a malfunctioning blower motor that isn't moving enough air across the heat exchanger.

Can I use the 18J28 to replace an 18J2801?
Yes, the 18J28 is technically identical to the 18J2801. They share the same 165°F/135°F temperature specs and the 7-inch probe depth, making them fully interchangeable.

How do I know if my limit switch is faulty or just doing its job?
If the switch remains open (no continuity) even after the furnace has completely cooled down, the internal bi-metal disc has likely failed and the component requires replacement. Otherwise, investigate airflow issues first.

Disclaimer: While we strive for 100% accuracy, product data and specifications are subject to change. Please contact our team to confirm compatibility or technical details before purchasing.