Are you using a thermostat or a rheostat with your UTH? If you aren't, make a quick trip to home depot and grab two things.
1. The accurite indoor outdoor thermometer. It is about $12 and measures ambient temp, temp from a probe, and ambient humidity. You can use the probe to measure the hottest point that your snake can get too. Right above the UTH under the substrate.
2. A piggy back light dimmer (rheostat). Many people get the lutron light dimmer that has a plug built in so you don't need to wire anything. Just plug the UTH into the dimmer and the dimmer into the wall. adjust the rheostat until your thermometer reads between 90-92* going no higher than 95*F.
Crusty scales sounds kind of not good. I would take the snake to see a reputable vet. They will be able to diagnose your snake better then a bunch of people on a forum using only a brief description.