Yes, Bottom one is used as the primary heating source. Top one is used to heat water if the hot water runs out.
Ok, you really could do with checking the current draw on the elements. Do you know how to measure amps and do you have any equipment to do so?
before you stick the probes of your multi,meter onto the terminals, show us a picture of the multimeter
Would you be able to treat yourself to one of these? https://www.tlc-direct.co.uk/Products/TMCMT01.html
Don't mean to butt in as I didn't read every previous post, but why not just replace the element again?