The valve needed to be energized for heating.

So on rth6360d1002-1738

Option 200 = 2

Option 205=7

Option 218 = 1

Option 221=1,1

Thanks for the reply. I forgot to mention but for the smart thermostat, when the heating did work, I had forgotten to switch it to heat pump mode (it was set to Conventional Forced Air Heat by default). When I re-installed the new one, I reprogrammed it to work as a heat pump to be used with B (i.e., energized for heating). I placed the white wire on W2 like it says on the manual (here) and neither the cooling nor heating worked. I then tried to replicate the default setting on the smart thermostat like when it did work previously and yet neither cooling or heating worked.

I just testing heating using the old thermostat via its programming and when I turned heating on, I felt air coming through the ducts but the outside condenser unit was not spinning. The air coming into the rooms was not warming anything.

I think I understand better. Dear Op, you may want to asses your skills before proceeding.

1) First if a difference between your current house temp and your call temperature > 4 degrees that system will call aux heat and your heatpump will not be running.

2) If a temperature outside below certain degrees, HP will go into defrost cycle before the outside HEAT PUMP starts.

You need to be able to check 24v telling HP to energize and 24v telling reversing valve to reverse. Wait for defrost cycle to complete.

You probably have a condenser starting problem and not a thermostat problem. The start capacitor may be failing and sometimes the condenser does not start when calling for heat. That could explain the blower running but the condenser is not supplying heat. When was the last time the condenser had a preventative maintenance check?

The Ameristar equipment is made in China and energises in heating "B" (like Rheem) not on cooling "O" (like Trane). Some older thermostats need a jumper between Y and W1 for heating to work.

I'd go back to square 1, wiring-wise with all wires connected as originally connected using the original thermostat. Your original thermostat was wired correctly (assuming it didn't need the jumper between Y and W). Don't go changing wires around if you aren't sure what they are doing. The fact that heating didn't work is a mystery, given that the heating works when connected to the new thermostat. The new thermostat has a setting for energising the O/B terminal for heating OR cooling. Make sure that is set correctly when programming.

You should see how the air handler is wired for the thermostat, not the condenser since the thermostat and condenser are not directly connected.

Y should be energized for both heating and cooling.

B should be energized for heat.

W should be energized during Emergency and Auxiliary, and defrost if you know when it is happening.

Sometimes a jumper is required between E and W at the thermostat (if the air handler doesn't have it).