Just had a new Trane system installed in October and it came with an XL824 thermostat. I live in Florida, so used the AC side for a few months without a hitch. When it got cold here in Jan (I know its FL, so don't laugh) I switched it over to heat mode. The air handler has an 8KW resistive heater in it. The air coming out of the vents is running at 90+ degrees when the heater is on. When I turned the system on the room temp was reading 69 on the thermostat and the thermostat target temp was set to 72. About 20 minutes later the thermostat is reading 70, so I'm thinking all is good. About and hour later the thermostat is reading 69 again, but its obviously getting warmer in the room. I use another thermometer to measure the room temp and its says the room is 73, but the heater keeps on running. So at this point I shut the system off. Over the next 1-2 hours the thermostat reading reaches 72 and the other thermometer also stabilizes at 72....so this is just the room temp stabilizing naturally with no fan running. Is there something quirky about the temperature sensor in the XL824 causing this in heat mode? I also thought maybe some kind of updraft going over the thermostat was the problem....so I tried setting my external thermometer right on top of the thermostat and it reads the same as when its just in the room ambient. Any suggestions or ideas why the XL824 temp sensor is acting flaky?