It's a bit like the older type of economy seven hot water tank with the top entry element fitting that takes an Old Type Double E7 Heating Element.
These Double E7 Heating Elements went out of production a couple of years ago, so it means you will probably need a new hot tank that takes the modern Side Entry Elements, once the old type Double E7 element fails.
Seen that one - Only has one thermostat, and not designed for ecomomy seven two-circuit use - must be wired through a common Bath/Sink switch control on ONE circuit, according to instructions.
It was also Old Stock being sold off...
With ref to earlier Proteus posts, i managed to find them on www.proteusswitchgear.co.uk , and it lets me order them on their site, or it says go to cef to get one, apparently they are still in the 2006 Proteus catalogue , will let you know whether they keep stocks of them!
iirc you can get contactors with double pole changeover contacts if so that should solve your immersion heater problem (use one pole to switch the heater on at night and one to put it into "bath" mode at night).
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