At first I thought it was broken and needed a new one but then I realized when it's shipped the thermocouple is not plugged in - make sure you plug it in! After that it has worked great. It's adjustable so you can do different diameter cups, mugs, and tumblers. I like to press it, rotate it, and then press it again to make sure it gets really good heat all the way around. Doing it that way I haven't had any issues!