Is Your Furnace Shutting Down After A Few Seconds?

Your flame sensor is a safety device in your furnace. It ensures the gas that fuels your furnace is being burned and not escaping into the vent system. In this episode, we’re going over the basics of your flame sensor. We’ll talk about catching a bad one and what you can do in a pinch if it fails.

The flame sensor detects when a flame is burning inside the burner assembly of your furnace. It does that by checking for a tiny change in electricity that fire creates. If it doesn’t sense that change, the sensor assumes gas is building up in your furnace and shuts it down.

To do its job, the flame sensor needs to sit in the flame. Over time the sensor will form a coating of black buildup from the fire. That will stop it from sensing those tiny electrical changes. When that happens, it thinks there isn’t any flame. It’ll restart your furnace a few times, then lock it down.