L.S.
You've gotten some good information. In my opinion, there's no such thing as night training at this age. How can you "learn" anything when you're dead asleep? YOu did the right thing by going back to diapers at night. Don't make this a big deal, because it's not. Staying dry at night has to do with the body's release of a hormone that allows them to hold it for that long at night. Some kids get this at 2 1/2 and others don't get this until 6 -- either case is considered "normal". This is not a behavioral problem.
Put a diaper on him at night and get some sleep. Eventually, he will wake up dry. When he does this consistently for maybe a month, then he's ready for underwear at night.