We have a Reliant electric hot water heater that is approximately 10 y.o. About 4 yrs ago, it acted up: giving is VERY hot water, and then kicking off .. reset button worked. We had to do that several times and were contemplating a new one, when it stopped acting up and held the temperature setting. Suddenly, it has started to do this again! It's been 3 days. Is there an internal thermostat that needs replacing? Or another sort of fix ... or is it on it's way out and requires replacing? Thank you!