The heater quit working on my 06 2500 cummins. As far as I can tell all of the doors are working and intact. A friend of my wifes said he took the hoses loose to and from the heater core with the truck running and heater on and nothing came out.

He flushed the heater core and it was clear, just nothing getting to it. I recently took it in to the dealer for a leaking water pump. After that is when I noticed the heater wasn't working. Is there a valve they could have turned off or a wire they may have left unhooked?

Any advice from someone with knowlege of the heating system would be appreciated as I doubt I have the money the dealer will want to fix it! They have allready told my wife it would probably be over $600 without even looking at it.