My 27 year old Carrier Super Saver furnace fan blower stays running even when the thermostat is off. After some troubleshooting, found out that fusible link connected to what looks like a limit switch P/N 4283A was blown. Replaced the fusible link, furnace ran fine for 15 minutes, then no heat, only cold air coming out of vents. Fan/blower keeps running. Whats causing the fusible link to blow. Filter underneath th
Your high limit switch may be bad, and need to be replaced.
Your furnace may be overheating, and the limit is not reacting. So the fusible link is doing just what it's supposed to.
There are a few things that can cause the furnace to overheat, a dirty filter being the number one cause.
Its not the flue pipe. That is a seperate circuit with a different fault code. If you have air conditioning, check to see if the evaporator coil is dirty. Your furnace goes off on limit due to lack of airflow. Therolloutswitch is a manual reset so if you have reset it the furnace would not uave ever come back on.