Ford Repair: heater will not blow hot, ford f 150, air fan

Question
i have a 2000 ford f-150 5.4 litre engine and the heater will not blow hot air fan is working fine hoses get warm changed the thermostat heater core does not leak any suggestions thanks

Answer
you have either of two problems, either the heater core is plugged or the blend door actuator is is stuck/broken- do you have manaual climate control.. ie. do you have to turn the know from hot to cold or does it have e.a.t.c. ie.. a digital read out ??