Replaced thermostat, New heater core few months ago. Everything works, the return and flow hoses to heater core both hot. No hot air what so ever. Any ideas?

 

Blend door functioning properly?

 

If I could check quickly without tearing dash apart again to get to the heater box, I would. Did test light the switch and good there, been chasing vacuum lines as well but nothing yet. Today after work I can tear the heater box out to check on the vent

 

Since your heater hoses are hot, there is flow through the core. Blend door issue most likely.