My 16 week old puppy is house trained and out of the blue he has started peeing in the house again. Could he have somehting wrong or is he acting out towards us?

There have been no changes in the house. He is alone for 8 hrs a day while we are at work. He is in his kennel while he is alone. He is up to date on all his shots and his last vet check was a week and a half ago.

Is your work day + commute 8 hours, or is he really alone 9 or 10? Were you rushing home right away at first, and now stop for an errand, or don't let him out the second you walk in the door? A puppy needs a mid-day walk, really. He also needs socialization with other dogs and people. I hope you consider a walker.
He could easily have peed once because he couldn't make it outside after that long, and then the floor had the smell in it, and that led to him thinking that the floor was OK. You have to scrub every scent out of the floor.