I have a tempstar heat pump It uses both gas and electricity to heat and cool. I put a new Honywell thermosta RTH6300B on the unit, now I don't get any hot air only cold. This I a four wire unit, red, white yellow and green. Anyone know why it won't heat, was working before but fan did not work that is why I put on new thermostat now fan works but no heat thanks for all the help

What's the old thermostat make/model and what wire colors were hooked to what terminal labels on it?