Simple question, but I've asked that to my mum before, but she can't
answer
that! The element was replaced without my knowledge about a year or so ago
at
some exhorbitant cost by some electrical/plumbing firm when the old one
went
short circuit and tripped the MCB.

Perhaps the installers were cretinous and replaced with a short element,
although the fact that the thermostat was 18" might suggest otherwise.

However, the amount heated by a top mounted element is never likely to be
good. I would recommend installing a new side entry element near the bottom
of the tank.

Christian.