I got a kenmore front load washer. As soon as I turn the hot water valve supplying the washer with the hot water, the washer starts filling up and won't stop until I turn the supply valve off

This would indicate at least two issues. Switches and solenoids turn water ON and OFF. Your solenoid is stuck open, bet it will fill even if you pull the plug and turn ON the water valve, try it and get back to us

Is this a new washer?

Here is the manual: https://dl.dropbox.com/u/8010163/Kenmore_Washer_Elite.pdf
You can disassemble that water valve and soak the parts in vinegar, then clean the parts. Your problem is most likely that a little hole in the diaphragm is stopped up which will keep the valve open. This happens on the hot water side more than the cold water side because when hard water cools it drops the calcium out of solution.