First of all, let me make it clear that some children still wet their bed at night at 8 years of age. Most of these children are completely normal and eventually grow out of this behavior. It is encouraging that he has constantly wet the bed, which usually is just a developmental problem that improves, rather than that he was initially dry and began to wet the bed again.
At the age of 8, most pediatricians would perform a simple workup of the bedwetting. This would include an analysis of a urine sample looking for infections or diabetes as well as a thorough physical exam. Sometimes this exam turns up something, such as constipation or another problem which can be contributing to the bedwetting. If your pediatrician
turns something like this up, they will focus on treating it. If not, then they will be able to talk to you about some behavioral techniques that you can use to help your child with bedwetting (for example, restricting fluid intake in the evenings). Usually these behavioral techniques work but, rarely, they may also suggest medications or other treatments.
Start by talking with your pediatrician, who will help to educate you about this very common problem.