My new apartment hot water system

17 Aug 2018
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United Kingdom

I'm trying to make sense of the hot water system in my new (second hand) apartment.
It's not like anything I've seen before. I know it's unvented, and the hot water comes out at mains pressure

Question 1: there are 2 mains boxes (heating elements) powered by different plugs - one feeding into the lower half, the other feeding into the upper. Wonder why, and what purpose each has.

Question 2: what's the small cylinder at the top for?

Question 3: the capacity of the cylinder says 210 liters. That's a lot for a small one bed flat - seems very wasteful for me to heat 210 liters everyday when all I do is wash about 3 dishes and take a short shower. There seems to be no option to only heat a small volume of water (no sink option).
Should I look into replacing this system with something else , this system was installed 5 years ago.


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1) The lower one will be connected to Economy 7 (if you have it) to heat up at night on the cheap electric. The upper one is a boost to be used if required during the daytime

2) It's an expansion vessel. It takes up the expansion of water as it heats. It should be checked annually as part of the service

3) The cylinder is well insulated so you're not heating the entire 210L every day, just topping up from what you have used. You could just heat the top half and leave the lower immersion turned off if you wanted, but heating the top half on higher rate electric is almost certainly going to cost you more than topping up overnight on the low rate. There's no point replacing it - you'll spend more than you save.
Next time you move home... Try looking for gas CH and DHW on the particulars BEFORE you take the plunge, if you are that concerned about such things :)

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