I'm getting 4 flashing lights from my furnace, meaning an open limit switch. It is -40c today so I'm wondering is it overheating and turning off just because it's having a hard time keeping up? Or is there an actual issue?


Check your filter for good airflow to keep cool. If possible, check you a/c coil to see if it's plugged or clean for good airflow. These things are free. If not, you may just have a bad limit switch.

Updated on February 7, 2018

Original Article:

How to Figure Out What is Wrong With Your Furnace
By Dan Robbins