Weekend house is 3 years old. We have Rennai instant water heaters. The diverter valve in one bathroom has good cold water pressure but as it is moved to the hot zone the water pressure decreases dramatically. The hot water pressure in the sink area is fine. Diverter valve is Moen. Is the valve bad or the hot water line clogged? This problem is only in this one bathroom. There is not enough water pressure to get hot water to the shower head.