Have HVAC Questions? Ask an HVAC Expert for Answers
Have you looked behind the thermostat to see if it is sealed up well behind the thermostat? It may drafting through the wall.
5 to 6 degrees is quiet a bit. There is an offset in the setup menu that allows a few degree either way to be displayed. You might want to check to see if someone may have set that. To do so, enter setup menu and scroll down to option 0700.See chart below.
Let me know when you are home and I will be glad to guide you.