is he in cloth or disposable trainers? If he is in disposable trainers, then he probably does not feel wet, or if he does feel wet, its not wet enough to be uncomfortable. If you can, buy a few pairs of cloth trainers or "big boy" underwear and either have him just wear those or wear them under pull-ups if you are uncomfortable with the thought of not using a pullup. He needs to feel wet fabric against his skin so that he feels uncomfortable and doesnt like peeing in his diaper.
also put up a sticker chart, everytime he goes potty/poop on the toilet he gets to put up a sticker, when he gets sest amount of stickers he gets to do a fun activity (but not until he has that amount of stickers) ex. playdough, go to the park, watch a favorite movie, etc.
one way of potty training that is super intensive is to just spend 3 days in your house, and have him only in big boy underwear. Feed him liquids, soups, juicy fruit, until he has to pee.....when he does pee if its in the potty, give him a little marshmellow, if its not on the potty, then make him help clean up. By the end of the 3 days, he may not be pooping on the potty, but he definitely should be peeing and you can gradually ween him of the treats.
hope this helps (i've potty trained 6 children so if you have any questions feel free to message me)
-J.