They just run hot. Not as hot as the 6011 mind you. It should still outlast just about anything out there. The nut that sticks out of the 6011 will burn you if you hold on to it for too long. The engineers at Burkert swear up and down that the heat they create will not harm the solenoid.
I was quite concern when I accidently touched it. At first i thought that maybe because I left it on over night. but when I had it on a timer going 2 hrs into operation it got hot. The milwaukee after 6hrs is not even warmed at all for the one I have. But, it's good to know that it's normal for the burkert to get hot and not defective.