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The B1370113 is a genuine OEM auxiliary (rollout/high) limit switch rated at 120°F for Goodman GMNT040-3 gas furnaces. This normally-closed safety control opens the gas or blower circuit when it detects abnormal heat, protecting the furnace from overheating. Replace it when the furnace short-cycles on limit, won't fire, or the switch fails a continuity test at room temperature.
The OEM switch carries the exact 120°F trip point and mounting profile the GMNT040-3 was engineered around. Generic switches with a different rating can nuisance-trip or, worse, fail to protect — always match the OEM temperature spec on a safety component.
Easy. Power off the furnace, remove two mounting screws, transfer the spade connectors, and secure the new switch. A quick 10-minute repair for most DIYers.