Do you have your Vamo set on OUTPUT RMS or MEAN?
If I'm not mistaken, you can find out by pressing and holding the left button for over 10 seconds. If it shows Output RMS, it means you were on MEAN. Leave it alone now that you're on RMS mode and from what I've read, Vamo owners solve this "heating" problem after that.
If your Vamo says "Output MEAN", it means you were on RMS. Do it again until your Vamo goes back to Output RMS. This would also mean that if it was heating up like that when you were already on Output RMS, I won't know any other solutions to help fix your heating up issue.
Hope this helps. I played with this issue a few days ago.