My State Censible 510E waterheater Model PRV 50 NORT B 32 CEW is not providing hot water the way it has been since I bought this condo in 2000. For example, when I fill up my spa tub, Iturn on the just hot water which gets hot quickly but which also cools off so quickly, that by the time the tub is full, the water is just barely warm enough to use. Is it time for a new water heater? This one was manufactured in 1991.