No heat after replacing thermostat and heater core

Hello, you replaced those components due to the heat concern, or because of some other reason? First, ensure all air is purged from the cooling system. This is really important. Next, you might have a climate control system problem, as the temperature blend door actuator may not be turning from cold to hot air, meaning no matter how hot your engine or heater core gets with the coolant, you may never blow hot air through the climate control system.