Left for the weekend and when I came home my Goodman furnace fan would not cut off. The batteries had died in my Hunter thermostat. I've replaced the batteries and it still will not cut off. What would cause the fan to stay on?

System went out on high limit causing the control board to keep the fan running.
Bad fan controler
Something wrong with the thermostat causing the call for fan all the time.

Turn off main breaker to furnace then reactivate and see if that resets the system.
Check air filters and replace if necessary.