Thanks for all the input. I really do appreciate it. I never had this problem until about a month ago. BTW, nothing has been changed in the house plumbing. After turning the temp down and replacing the pressure relief valve, the problem wasn’t nearly as bad, BUT, it still will occasionally overflow. Can a water heating system suddenly develop a thermal expansion problem after all this time? The temp of the water escaping is about 140 degrees, the temp it used to be set at.