1. The wall tstat does state HEAT PUMP? Not heat or Electric heat
2. There are only 3 wires to the tstat. If either of the wiring is wrong the tstat will not work at all
3. Are you POSITIVE you have connected all the control box wiring correctly?
4. The default on new Dometic HP's is to cool. It takes power to energize the reversing valve to heat. That means in COOL mode the reversing valve is energized and in HP mode it is NOT.
What do you mean by DEMO model? Never heard that term before as it relates to RV AC/HP units. Doug