How long does it run on heat? Does it reach the set temp and cut off the heat but the fan continues to blow?

By aux heat, do you mean the emergency heat position that disables the heat pump?

It may heat for an hour or so and never reaches the desired temp on the thermostat. Yes...aux is emergency heat. wHEN ON EMERGENCY HEAT THE OUTSIDE UNIT GOES OFF LIkE IT SHOULD AND WILL HEAT WITH THE INSIDE HEAT BANKS AGAIN FOR AN HOUR Or SO BEFORE IT STARTS BLOWING COLD AIR. Then if switched to heat mode it willl again heat for an hour or so before blowing cold air. NEVER REACHES DESIRED ROOM TEMP

Could be an over temp limit switch tripping due to low airflow, or a bad limit switch. Do you seem to be getting full air flow?

yeah the airflow seems to be just fine. As far as reaching room temps it will reach the desired temp if the initial heating cycle brings the temperature of the room up. But after a while in both the emergency heat or heat mode the heating will diminish until cold air comes out reducing room temps. We are presently going from heat cycle to em heat cycle back to heat cycle etc to keep the house warm

Do you have a battery operated thermostat? If so, checked the batteries?

yeah I do......probably havent been changed in years. A new thermostat was installed about 5 years ago and Im quite sure the batteries have never been changed. Could it be as simple as that? If so...could you explain why??

Re: explain why it could be the batteries.

I have no specific reason, except when you have a "crazy problem" like you say, I like to see as many variables as possible eliminated.

Emergency heat couldn't be simpler and yet you are having trouble with it. Really, electricity flows through special wires and makes heat. I was looking for something in common to both heat pump and emergency heat, so why not try new batteries in the thermostat. Easy for a homeowner to try and go from there if it doesn't work.

yeah I do......probably havent been changed in years. A new thermostat was installed about 5 years ago and Im quite sure the batteries have never been changed. Could it be as simple as that? If so...could you explain why??

How crazy would it be if that was the problem. Does the thermostat and batteries have to have a certain voltage or amperage in order to properly perform its functions?? Do the batteries have to constantly throw a current that the heat pump would need?

The thermostat is nothing more than a switch. On/off