Heater inop

Your upper radiator hose is supposed to be hot, and so is the bottom. When the thermostat was changed, did they bleed the system of air? Because this can be your issue if air is trapped in the heater core.

If that's good, then your issue is either a stuck control shut off valve, blocked heater core, Stuck/broke blend door inside the HVAC unit or a leaking vacuum line/solenoid in the HVAC unit.

The shut off valve is located on one of the small diameter coolant hoses that enter and exit the firewall on the passenger side. It's a small metal valve with a linkage hooked to it. Once your engine warms up, have someone turn on the heater controls (high) and watch the movement of the valve.