Are you sure the part is bad? If it is shorted then you know it will pass current until you heat it to the cut-out. If open, you will get to hot water. Did you ohm the heating element? They can burn open over time. I have fixed a number of them for friends and all were the heating element, not saying your cut-out is not open, but check it with a meter. The home improvement store will not check it, but they will sell you all the new parts you need until you fix it.