I have exactly the same problem, it comes on and then after a few seconds, or sometimes a minute or two, its as if it changes its mind and just switches off. I have had the dem 10 for about four months and it has been great, the house is warm enou for it to work and we have plenty of moisture in the air for it to work on-we use one of those tent like clothes dryers from china and it produces a lot of moisture, so it can't be that there is no humidity.
Matt, April 2013