My dog is crate trained and has always been very good. In the past week, he has been peeing in his crate and is always very thirsty... what is his problem?

Could be diabetes. There are other things it could be too. I would not even try any training techniques until a vet gives him a clean bill of health.

Yup, time for a vet visit. It could be a simple urinary tract infection that can be cleared up with medication. Whatever it may be, when your dog is exhibiting behavior out of the norm, it is time to make an appointment with the vet for a health check.