Just fixed this problem with my DES14. Its a fault with the circuit board inside the machine and is very easy to fix, even for a novice. Here is how to do it:
1) Open up the machine by removing the screws in the case. (Make sure it is unplugged!)
2) Locate the circuit board on the side of the unit.
3) At this point you have two options. If you want a unit with full functionality you need to buy a replacement circuit board. I found one on MasterSpares (http://www.mastersparesonline.com/product/index/10147)
It costs about 30 pounds. Simply remove the old board and replace it.
4) If you want a working unit for no extra cost (but without the functionality of the humidistat) then remove the rectangular white connector from the circuit board which has red,blue,white and yellow wires entering it. Add an extra wire between the central white wire and the red wire that is adjacent to the yellow. (see photo).
5) Re-assemble the unit. If you have opted for the free option the unit will work when you plug it in and switch it on but will no longer cut in and out with different humidities (or have the annoying warm up period). Thankfully the water overflow cut-out will still work.
Hope it works for you! Feel free to ask if you are confused!