06 Subaru Legacy 2.5 has NO HEAT after head gasket replacement, coolant flush, & thermostat change. HELP!

Hello, as the title says I have a 2006 Subaru Legacy 2.5 I’m having issues with. The car is only blowing out cool air while the heat settings are on high heat. The car has appx 175k miles with record + receipt of the head gasket being replaced at 140k miles. The coolant in both the radiator and overflow tank are completely full + the car consumes 0 coolant - I’ve never had to add or “top off” the radiator/overflow. The car had a new thermostat put in 2 days ago accompanied with a full coolant flush. The car still only blows out cool air…WHAT COULD THIS BE?!? Is there any type of blend door under the dash that fails to open/close? (Theres no sounds coming from dash area) What can I be missing? Thank you for any logical input.