Below we have a real good YouTube Video made by GrayFurnaceMan that shows how to troubleshoot a gas furnace limit switch on an 80% AFUE furnace. Thanks to GrayFurnaceMan for making this informative video. Please click here if you are interested in the name brand furnace limit and rollout switches that we sell. Please email us anytime if you have questions. Our email address is: email@example.com. We would love to help you out and have your business!