DIY & Home Improvement

Based on the house overheating. The unit will only do what the stat tells it do do. Get a thermometer. If your unit is still running when your house reaches the temp you set + or - a degree or so, the stat is bad. You can replace the stat yourself but when you remove the old stat make sure you write down which color wire goes to which terminal and replace them on the same terminal with the new stat. Also, be sure you turn off all the power th the system or you will fry your transformer.

Edited to add, check the temp right where your stat is. The stat only knows what the temp is at that exact spot. It has no idea what the temp is in, say, your kitchen. Also, make sure the new stat is for a heat pump. Stats are different for different systems.