1996 Ford Explorer no heat in cabin

Heater controls work, defrost, vent, ect.
can hear servo motor work when adjusting temp control.
vacum switch working on heater hose junction.
hoses to and from heater core too hot to hold
engine temp ok. Had to drive vehicle home when this first happened, 65 miles, four or five stops with engine off, engine ran fine, check engine lite came on once but went off, coolant is full.