Water Heaters - water too hot

Our household electric water heater, a 50gal Reliance brand, fairly new, all of a sudden is heating the water way too hot. I had not turned up the temperature control for either the lower or upper element, so I am wondering what caused the sudden increase in the temperature of the hot water. My wife noticed it first at the kitchen sink, where if the hot water is turned on it will get steaming, scalding hot. I checked the other faucets in the house, and the water temp gets way too hot now when the hot water is turned on.

Don't know whether it has anything to do with it, but the night before we noticed this increase in the temp of the hot water I had switched the hot water heater breaker switch back to on after turning it off for six days while we were away from home on a trip. But all the time prior to that the water temperature would get to only about 125 degrees or so, set close to the lower end on the thermostat controls on the heater.

I double-checked the thermostat settings for the upper and lower elements of the heater. The settings on the dial don't actually give specific temperatures, but instead have a graduated scale that goes from the lower point called "hot", then higher to A, then B, then C, then finally to "very hot." The controls are set at the lower end, toward the "hot" setting, yet still the water heats up to scalding temp.

For now I went ahead and turned the breaker off, thinking if it just keeps getting too hot it might pop the pressure relief or something and I'll have a big hot watery mess on my hands, or something worse to contend with.

What may be the likely cause(s), and what can I check or do to fix this problem?

Most likely reason is you have a faulty thermostat that is not opening the circuit at the proper temperature. I would recommend changing both upper and lower thermostats unless you can positively determine that it is only one of them.

Most likely reason is you have a faulty thermostat that is not opening the circuit at the proper temperature. I would recommend changing both upper and lower thermostats unless you can positively determine that it is only one of them.

Thanks furd. Until I get a chance to change out the thermostat(s) is there much possibility that the water will get so hot the pressure relief valve will release, or perhaps other damage of some kind can occur? Should I just leave the breaker off to the heater for now, for safety, or is there usually some kind of high limit point at which if the temp gets too hot it will trip out? In other words, is it probably okay to leave it on so we'll at least have hot water until I replace the thermostat(s)?