First kill the power to the wh. Then take the covers that cover the thermosats off . Remove the plastic sheild then take the wires off the element . Put your electrical tester on buzz(there is a setting that buzzes when you touch the probes together).Or put on ohms. This proves conductiveity. Touch the wire terminals ,it doesnt
matter which color you put on what since its 220v. If it buzzes the elements good if the needle goes up its good. If it doesn`t its bad.
If you got a little hot water its probly the bottom element.
if you got no hot water its the top.
If the water is normal one minute then steaming hot the next the bottom element is probly in lime ,There really not a good way to clean one out.
To help prevent lime up ,Wait till someone takes a shower or bath then drain the water out the rest of the way down. This will help prevent lime up, ecspecially if you don`t have a water softener.