I noticed on the news last night that the inquest is under way on that
awful case of the baby who was scalded to death a tear or so back, when
a tankful of boiling water came through her bedroom ceiling:

http://news.bbc.co.uk/1/hi/england/somerset/7175037.stm

The TV bulletin helpfully showed a clip of a reporter sitting in an
attic next to a plastic CW tank, and explaining how 3.5 million homes
are potentially at risk of a similar disaster.

Visions of half the population phoning their plumbers this morning to
come and do safety checks...

I'm not familiar with these immersion heater systems, but as the owner
of an unvented gas-fired system whose emergency overflow has the
overheated hot water dumped outside the building at ground level, isn't
there something fundamentally a bit nuts about a system which is
designed to dump it above the ceiling into a plastic tank which is
melted by boiling water??

David