Every once in a while, Mitch likes to bring out the camera while doing on-the-job training. Here, you can watch Chris demonstrating the proper way to test a limit or flame rollout switch with a voltmeter.
Limit switches are furnace safety switches that trip-open when they exceed the temperature that they are designed (this varies depending on brand, location, and type of switch inside the furnace). Limits are designed to shut down the burners in case of a malfunction of the unit. While some automatically reset (they open when the temperature they are designed for is exceeded and close when the temperature drops below the design temperature), others are manual reset (they open when the temperature they are designed for is exceeded but have to be manually reset or the unit will not operate). When on a no-heat service call, limits are one of the first things we check, and during your heater maintenance, we will either manually trip and reset your limit to check that it's functioning properly, or use a temperature probe to check at what temperature your limit is opening.
So without further ado, click below to watch Chris demonstrate how to test a limit!