Heater blowing out cold air in 2000 Chevy Malibu?

[heythereamberr]

The owner before us used stop leak and didn't properly drain it out so we have paid the price and keep having to flush the radiator. We got a new low mileage engine put in and the heater started working again and it didn't run hot. After I got my a/c fixed this summer it started running hot again and we have since replaced the heater core and thermostat and it once again is running hot and the heater blows out cold air. Also there are no leaks coming anywhere from the car. I don't understand what could be causing this. Any thoughts or suggestions? Please help!

 

[Micheal Caffery]

Check:
That you have coolant
That your repairs were actually made and they are still working
Water pump

Also make sure you let the engine warm up, then take it to a repair shop and tell them to fix it