What is a Rollout Switch?

Your furnace is full of sensors, regulators, switches, and detectors of near everything. There are flame sensors, temperature sensors, pressure switches. That’s a lot of stuff that mostly feed into a controller that operates the furnace as long as it sees all the right readings. That one device is an almost single failure point. The only good way to stay safe is with redundancy. In most cases, these are physical, mechanical safeties which will over-ride every other part of a system and force it to stop cold. Cutting Power on Failure The Roll Out Switch is in simplest terms, a very fancy fuse. Most furnaces will have several of them spread throughout, each tuned to a particularly temperature. One near the burner or heat exchanger may be designed to trip if the furnace exceeds it’s maximum rated operating temperature. Another near the controller board may be set much lower, perhaps around 90 degrees celsius, just shy of when most silicon chips start to fail. Some may rest near the fuel line and manifold, set to extremely low temperatures, in case a leak and fire occurs away from the burner. In the event that any of these switches trip, all power to the furnace is cut. There’s no shutdown process, it just loses all electrical power. If things were going wrong or at risk of going wrong, this usually stops the problem dead in its tracks. A shut down furnace cannot […]

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