Central heat is blowing hot and cold air.
Hello, I just moved into a new home that has central air/heat. When I turn the heat on it blows warm air and once it reaches desired temp starts to blow cool air which then forces my heater to be on all day/night long because it can not maintain the temp. I am spending more on heat than I do on AC in summer. I've changed the filters. Do I need to call a technician? TIA