Goodman power vented multi-position gas furnace fan won't shut off. Only way to shut it off is at breaker box. Do I need a new thermostat?

No you probably need to reset a limit switch. What is the red light flashing in the bottom door??

Not sure, I opened both doors and checked the thermostat, It has been working right ever since.. I have 2 units, one in basement one in attic. The unit in basement has a filter attachment for it, the one in the attic does not. Can I just slip a filter into the duct or do have to put in a new section to hold the filter.

Thanks again