2012 Explorer Heat Issue

[nadorp]

Well, to re-emphasize, if the hot coolant isn't circulating through the heater core, the temperature blend door doesn't matter.

Correct!
It is "assumed" by a Ford mechanic, the issue must be in the thermostat area. I replaced the thermostat with a new one last summer that I checked in a pot of boiling water before I installed to make sure it opened and closed at the right temp. I think replacing it again may be unnecessary but who knows. Maybe a plug in one of the lines coming off the housing? May have to take them off and blow pressure through them. The problem is definitely not in the vehicle.