My electric water heater suddenly and with out warning starts to put out very HOT water. This is soon followed by no hot water at all. I checked the breaker and it is ok. Opened panel on water heater and pushed red reset button on upper thermostat and heater started back up. It acted normal for about a month then suddenly the hot water is back again followed by no hot water. It has two thermostats but only one (lower) is adjustable. It is set on 120. Help!