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The Lennox 20W36 (OEM part number 100847-04) is a genuine single-pole single-throw (SPST) control limit switch rated to close at 150°F, designed to protect your Lennox furnace from dangerous overheating conditions by shutting down the burner when temperatures exceed safe thresholds. If your Lennox furnace is short-cycling, failing to ignite, or triggering a high-temperature lockout, a faulty limit switch is often the cause. This OEM replacement switch ensures proper fit and reliable performance for compatible Lennox heating systems.