I have a new 50 gal electric water heater that I bought from Lowes less than 6 months ago. Over the weekend I noticed that the water was only warm (90 F). I checked the resistance on the elements (both read 13 ohms) and voltage to the upper element (240v). If I turn down the thermostat to the minimum the voltage swaps to the lower element, as expected. Even so, I swapped out the upper thermo and element, no change. Yesterday by accident I discovered that as soon as I shut off the cold water the upper element starts percolating. Turn it on and it stops. I can't figure this out. The unit is under warranty, but the manufacturer (US Craftmaster, dba Whirlpool) does not answer their tech support line. Suggestions?