This problem has defied all explanation.

I have replaced both thermostats - the upper and the lower - with the
exact same model that the unit had - and the red button tripped again!
So by process of elimination, I have to replace the elements now. I
have no problem doing both but I've never done this before. Do I just
unscrew these things or do I have to drain the tank? Any instructions
would be appreciated. Thanks once again.