I have a pressure balancing Moen of some sort - can't see the number but it looks similar to 3550 and has been installed and working for many years. Problem, even when shut-offs are on, no water passes through the tap. It also doesn't pass any water with the cartridge removed. On either side are sloted contols with spring loaded cones - anyway they dont seem to be the problem. And at 10PM i didn't have a device to open the large sloted whatever.