I am replacing thermostats and having problems with emergency and auxiliary heat. The T841A1712 used W2 and E terminals, but the P374-1700 has only a W2 terminal and manual indicates it uses W2 for emergency heat.

I have tried putting both wires on W2 as well as each wire by itself without proper function, I get only a momentary burst of emergency/auxiliary heat.

This is a heat pump system and primary heat/cool is working. I also have an occasional problem with defrost of the outside unit, but I suspect that is another problem entirely.