My heating unit is about 14 years old. Earlier in the week the weather was 70 degrees, today it's down to 26 degrees. My heat is on however it's blowing cool air as I have the thermostat set around 66 degrees. When the auxiliary heat kicks in, it gets warm. Also, it seems to run constantly. I don't remember this happening before when it was this cold. Once the house reached a certain temperature, the unit would kick off. So far it's ran all night and all morning. Please help! I don't want to call someone out and get ripped off. Thank you!