BTW, I mentioned that I checked online to get a price on a Rheem 50 litre mains pressure electric hot water system - most sites quoting $450 - $480.
I called into Hardware & General this morning - $365!!! Moral of the story - sites called "cheaper hotwater" or "discount hotwater" are not necessarily so.
Anyway, until the sparky checks the house on Thursday, I wont purchase a new hotwater tank until I know that it is really the problem.