See folks, an instant electric shower /can/ beat a high flow combi :-)

You can get 24kW instant electric heaters, provided you can spare a 100A
phase for one. I wouldn't attempt to apply diversity given that it will draw
the full 100A when operational. Alternatively, I believe you can get 3 phase
ones that will only draw 33A off each phase.

These could be a good solution for a shower liking person with lots of
electricity and no gas or oil. They would be particularly suitable for a
holiday house that is left unattended, as water tanks can be a worry for
leakage and accidental heating for long periods (such as over winter).

Christian.