Light does not come on as it is described in manuel. The wiring diagram shows an orange wire and the heat system is gas. Is there such a system as a gas heat pump.???? There is no orange wire from the existing thermostat only white ,red,green,and yellow. the thermostat seems to be funtioning ok, ie. heat when called for comes on but the air doesn't seem very hot. The heat (gas) is on and visibly burning. could this be the wrong thermostat model. Maybe should use the 8363??