Backflows stop backward movement of water into the city(well) water supply. So
the first thing that comes to mind is we discovered fire, so let’s make the water warmer. Since we don’t heat the water over fire and put in it a tub, we have water heating tanks and as water is heated in them the water flows backward into the city main lines, the backflow device stops this. With this backflow stopped the pressure in your increases to dangerous high pressure. A residential plumbing system is only made to handle around 80 pounds of pressure . Therefor you should have some sort of thermal expansion control device installed. Please confer with your plumbing company about this and its maintenance. Proper knowledge of the one installed at your location is the owners responsibility.