Well I don't know, but we have central heating. Turn it on and the rads heat up and you have hot water through the immersion for several hours. I would usually only boil a kettle for tea or if I need to, um, clean Karen up. And for boiling things afterwards. Otherwise the hot water comes out of the taps once the heating has been on for about an hour.
Funny(ish) story: we used to have to turn off the immersion or the water would just keep getting hotter and hotter, on the old system. And of course everyone forgot. Cue someone jumping in the shower and howling in pain as scalding water hit them! "Who the **** forgot to turn off the immersion? AGAIN?!"
