: My 5 year old 80 gallon electric water heater suddenly started to heat the water much hotter than : normal. It stopped heating all together so I flushed the tank, : pushed the reset button and I can hear it heating. My question is now what do I do? Does the thermostat : need to be replaced or is it the heating element? How do I know? It sounds to me that you need to start by replacing the heater elements. Its not to hard, but you need to turn the power off I say again turn the power off, than drain water heater and remove the top and bottom cover plates you will then see a big nut that has two wires red and black, remove the wires and loosen nut. the element will side out and the new element will go into place, do the same on the bottom and your done. Oh be for I forget you can buy a element tool ,to remove that large nut its cheap. also be very careful if you are not up to it call a plumber sametimes we can save you money and save you from beating it with a hammer. will best of luck