I have no heat in the cab on my 2007 ford F250 diesel 6.0 L. I changed the potentiome that regulates the flow of hot and cold and it did not change anything.
When I leave it idle it does give a little bit of heat. What else could I try?

Tony

Fords have a very fine mesh in their heater core. Feel the hoses at the firewall. If they are both hot, with the control set to heat, you have other issues. If one is very hot and the other not, you most likely have a plugged core. Disconnect. The hoses and back flush the core. Last one I did yielded a cup or two of gunk. Heater worked fine after that.