Could a clogged for bad thermocouple cause a furnace to run continually even after it reaches the set temperature on the thermostat? The furnace does not continue to get hotter - seems to send cooler air once it reaches the set temperature.

No,, the job of a thermocouple is to keep the pilot light burning

Check and make sure the tstat is set on Auto,, and not on fan/fan only setting

, and get to us

It is set on auto. The fan runs continually and can only be shut down by unplugging the unit. I have even tried turning the thermostat down 10 degrees but it still runs.

Take the cover off the burner compartment of the furnace. Obtain the make and model of the furnace off the rating plate in the burner compartment and post it here.

Observe the sequence of events that occurs at the furnace when you turn up the thermostat and post that sequence of events in order and in detail.

The furnace has been working fine since I got home from work. It did this same thing several months ago. If (when) it runs continuously again I will post the information requested. Thank you so much for your help to this point.

Help - it is running continuously again!! It is a Lennox G20RQ3/4e-100-1. When heat is turned up the damper door opens, there is some clicking (igniter?), the furnace lights and blower comes on. When it reaches set temperature, the burner goes out, damper door shuts and blower continues to run (until I have to unplug it to turn it off).