I have a heat pump system,and for the past few days I've noticed it will not shut off when it reaches the desired temperature. I have a Honeywell RTH3100C non-programmable digital thermostat, which we've had for about two years, and everything was fine until now. If the thermostat is set to 72, and the inside temp reaches 72, it won't shut off unless I bump it down to 70 degrees. But then it kicks on later at 70, and does the same thing... won't kick off unless I bump it down a few more degrees. Right now the thermostat is set at 70, and the room temp says 72. I set the thermostat to 71, and the heat kicked on, even though the thermostat says it's 72 inside. What's going on? Help!