I did too. Twice. See here: http://www.fordraptorforum.com/f10/2010-ford-raptor-seat-heater-drivers-side-hot-spot-9033/
But the bottom line is that your heater element has shorted. Its turning off because its detecting an interruption in the circuit, and if left on it will, quite literally, start a fire.
Get it replaced under warranty, and cross your fingers it stays working. Mine didn't and again needs to be replaced (of course, this time I'm not under warranty).
Mine crapped out twice also. Must be all the talking out of our asses we do.
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