Lennox International came into being in 1895 when founder Dave Lennox invented, manufactured and marketed the world's first riveted-steel furnace. Today, Lennox International manufactures a line of gas, oil and electric furnaces for residential customers in the United States. If your Lennox furnace overheats or experiences a similar malfunction, a safety component known as a limit switch may cause the appliance to turn off automatically. It's simple to reset a Lennox furnace and have it working again in seconds.
Switch off the electrical supply to the Lennox furnace from your electrical service panel to eliminate the risk of electrical injury during the resetting process. Flip the circuit breaker switch labeled "Furnace" or "Heating System" into the "Off" position and leave it there.
Take the control access panel off your Lennox furnace. Note the the location of this panel varies; it is the bottom panel on downflow furnaces and the top panel on upflow furnace models. Lift the control panel up and away from the appliance; set it aside.
Examine the exposed furnace components. Look for a raised button or switch to the right of the furnace's ignition control box; this is the "Limit Control" switch.
Press and release the "Limit Control" switch to reset your furnace.
Reverse the removal instructions to replace the furnace control access panel. Return to the electrical service panel and flip the "Furnace" or "Heating System" switch to the "On" position.