Problem with Heater

[rksorrells]

I have a 2008 F250 with about 120000 miles on it. With the engine warmed up I can turn the heater on and it will blow hot for about 30 seconds then i get nothing but cold air. I tried searching for posts concerning heaters, however everything I found concerned the 7.3 or the 6.0 engines. Does anyone have any ideas of how I can remedy this? Does anyone know if the 6.4 has a vacuum controlled heater valve similar to the 6.0? Any help is greatly appreciated. Thanks again

[blackcloud2k]

do you have the dual climate or the normal knobs? Could be blend motor gone bad. I have seen it on the AC, but not with the heater though.

[rksorrells]

I do not have duel climate control. Just the old fashion knobs.