So the way I understand it is that a heat pump will operate in heat mode until it gets too cold outside and then the gas furnace will take over. I did an inspection a couple weeks ago with a heat pump and a gas furnace. The thermostat was one of the old mercury types with three sliding levers. I could get the heat pump to work but I did not know how to get the gas furnace to fire. I am sorry for being green but i dont know how to get it to fire without an emergeny or aux heat button.
My advice is to take the make and model number down and do some research on how they work (owners manual) If you can not find an owners manual online contact that manufacturer tech support and ask the questions you need answered. I have done that many times in the past 8 years as I can not possiblly know how everything that is manufactured operates and many appliances/systems have crappy web sites for installation and operation.
just my 2 pennies Juan
there should be a lever that says “emergency” heat, flip that one on and the gas furnace should be your first stage heat.
the reason you got no gas furnace in regular mode it the fossil fuel kit was keeping the heat pump on as it was not cold enough to bring on the furnace.