Rheostat trouble?

[Jo060]

Hey. I bought a Rheostat yesterday for my UTH because my UTH was getting WAY to hot (111-117 degrees F.) So, when I hooked the Rheostat to the UTH I put it to about med. and it was still MUCH too hot. So, I tunred it all the way down to low and its still too hot staying around 97-100 degrees F. So, today I bought a piece of lenolyom (SP?) and but it under the substrate and its still reading like 97 or higher WTF AM I TO DO IT's DRIVING ME CRAZY!!!