Wallpaper was removed from our living room by a "professional" and the walls painted. The paint peeled in large pieces in several areas within a couple years. We had another painter scrape and repaint. This second guy thought the wallpaper paste had not been properly removed. A few years later it peeled again. This time I'm scraping it. There's no evidence of moisture. It's peeling right down to the wallboard and the wallboard looks clean. I noticed that most of the large peeling areas are above the heat registers. Never heard of that causing paint to peel. How do I make sure the paint will stick this time? Will a primer be enough? How do I know there is no residual paste?