Stable performance, high accuracy, small size and light weight. 31091 limit switch is a very important safety device on the furnace to protect it from damage, this device should always be closed and when the flue temperature in the heat exchanger becomes too high, the limit switch will immediately shut off the burner to prevent overheating. Note: Limit switches with multiple temperature ratings are located at critical locations above the heating chamber of various furnace models. It is very important that when replacing one of the switches, use an appropriately rated switch.