My heat pump works fine in both the first and second stages, but when the temp in my home reaches the temp set on thermostat the heat stops but the fan never does. It just starts blowing colder air until I set the temp down further or just turn off the heat. I don't mean blow for a few minutes but rather hours or howerver long it takes before I shut it off. Anyone know what's up with this and how to fix it. Unit is brand new too.
Thank You

If it is a brand new unit then it is under warranty and I would call the company that installed it so they can fix it for free.

I called them first but they said it would be a day or two so if I could easily take care of it myself I will. They have already come and changed the thermostat thinking that was the problem.

You are better served by having them do the work. They can void your warranty if you mess with that new furnace since you are not factory trained etc. Since the problem could be with the wiring or a bad part you do not have access to the test equipment or the parts if you found the problem anyway that is another reason not to mess with it.