said by John97:
Thanks for all the replies.
I do have low-flow water-saving showerheads. I replaced all three showerheads in the house the first week I was here because a) they were all beat, and b) the house has a septic system - so I want to do what I can to minimize water usage.
Even with the low-flow showerhead the hot water only lasts between 5-10 minutes.
I am going to give the warranty company a call today after work and lay this all out to them, to see what they say.
It sounds to me that your lower element(s) may not be working. That would account for the very limited amount of hot water. It doesn't take much for the upper element to heat the water (at the top of the tank) and cut off. More than half way up the tank the water will be very cold.
Normally unless you dray a lot of hot water the bottom element does 90 percent of the heating. The top element basically is to provide hot water as long as possible if the temperature at the tank top drops to actuate the top element and turn off the bottom element.
I have mine set at 120 degrees and it's plenty of hot water for my wife and I to shower for as long as we want.