Underbelly scabbed up and snake wont eat

[Tiny Boidae]

Poor little fella! A vet visit is absolutely 110% mandatory at this point, otherwise that snake will probably end up dying. As others have said, get a thermostat for the UTH and don't just unplug it. What would also probably help is getting out the wood chippings you have in there now and do a really good scrub down of the cage to get it as clean and sterile as possible. Instead of replacing it with more wood chippings, I would use paper towel or something similar. While he's being treated, clean the cage weekly or anytime he soils it with the use of reptile-safe disinfectants. Also, make sure the humidity stays up but don't soak the substrate as that would only aggravate the problem.