Are you sure your flexwatt is actually heating up? Does the Helix give a read out of the amount of power being delivered? I had this happen on one piece of flexwatt; my Herpstat kept saying 100% output, but it was only getting to ~80; which was the ambient temp anyways. Turns out I had a poor connection. I re-soldered it and it worked, and is working, perfectly at its correct temp.