Are you running a herpstat 1,2, or 4? If you're running more than a 1 make sure you're plunged into the side you are using your prob on, also make sure you programming corrispons to your desired temps.

I.E make sure your using prob 1, that you UTH is hooked up to outlet 1, and that you have it all set on configuration 1.

If this doesn't fix the issue, just plug the UTH into a wall outlet to make sure it heats up and is working correctly.

if it heats up and isn't working on the HerpStat, take the fuse out and make sure it's not blown.

If this doesn't help, send pictures of your set up. And some more info