I have a 53 gallon water heater which should be plenty for a household of two. The problem is that just 5 minutes into a wonderful steaming hot shower, the water would suddenly become just warm and I would need to turn down the cold water to keep it hot. I thought the possible cause would be that as hot water is drained from the heater, it's filling with cold water at the same time so the water inside the tank gets cold. Or maybe there's something else. Could anyone shed some light as to any other possibilities?