I am having an issue with my hot water flowing slowly. The lines(copper) are in the floor(slab) and the WH is in a non-heated room. The problem only occurs when the outside temp is around 40 or lower. It seldom gets below freezing. I am replacing the WH next week with a Rheem 40gal, but should I be looking for other problems? Also, the WH is installed backwards in a corner (cannot get to elements or valve), so I assume it has never been cleaned. Only owned the house for 2 years. Any help is greatly appreciated!