Honeywell limit switches are safety devices used in furnaces and water heaters to protect the units from dangerous temperatures. The switch shuts off gas flow if a preset heat is exceeded and reopens the supply after reaching the lower-limit temperature.
These electromechanical devices use momentary contact to close and open the gas valve. This helps avoid damage due to overheating when airflow is restricted. Clogged air movers or dirty filters can cause the switches to trip, and they can fail after repeated power cycles. Defective or broken limit switches are relatively easy to diagnose and repair for the average homeowner.