Lennox furnace error code 551

If you’re getting error code 551 when you start up your furnace, it can mean that the limit switch circuit is defective. The limit switch is typically found on either side of the air filter case. Try replacing the limit switch and then restarting your furnace to see if it fixes the issue or not.

If you don’t know what the Lennox furnace error code 551 means, you should read this article.

The Lennox furnace error code 551 is a considerably easy standard in order to understand. It typically communicates that the system has shifted out of the heating mode and into cooling mode. This can happen if the outside temperature drops below 45 degrees or rises above 90 degrees.

In a Lennox Furnace, there is a heat pump and an air handler unit in which heat is delivered to your home by exchanging hot and cool air from one system to another. If the outside temperature is below 45 degrees, then by default, your furnace will turn on its heater (in heating mode) to push heated air throughout your home so that it can provide an adequate amount of warmth.

Lennox has a list with all of the error codes that can be displayed on their furnace. The error code 551 is typically displayed when there is a problem with the flame sensor. The flame sensor may need to be replaced or have its wiring checked out because it can’t get enough power to operate.