Can anyone tell me about my 210L Megaflow?

[StoneBasket]

Moving house I've inherited a tall 210L Megaflow with two large grey plastic squares on the front. The lower of which is wired to the boiler. The sticker on the front of the Megaflow says it's 3kw + 2.7kw, so two heating elements I presume. My electrician says he's worried because the top element isn't wired in too & it should be for full functioning. My heating engineer says the top square is just a 'blank' if you wanted to add a 2nd element in and that there's nothing underneath it. Is this true do you think?

I also have a 210l megaflo.

Mine has two heating elements - one under each of the grey covers.

Is it possible one of yours has failed and they just removed the electricity supply to it?

The idea is that you use the bottom element most of the time and the top one if you need a quick boost of hot water. Mine, however, got wired up wrongly at some point in the past, and I can't be bothered to get an engineer out to change it round. it works fine but I think I probably have slightly cooler water in the tank than I otherwise would as it only gets heated from half way up.

Mine has two elements but I think that is because I am on Economy 7 and it uses the second element for that.

I’ve got a similar system which I love but mine was also wired in wrongly for years before I got a new engineer to service the boiler who noticed it. In my case it was something about it firing up the boiler more frequently than it needed to. They’re still not that common and it’s not easy to find someone who knows what they’re doing. When it does go wrong it’s very expensive to fix.

How often do they need servicing please?

Mine used to need servicing once a year but the airgap needed replenishing roughly once every 6 months.

I struggled to find anyone local to me who knew how to service it so I used the manufacturer (vaguely remember they trade as Heatrae Sadia) to service and repair it. They charged quite a lot, but you cant afford to muck about with an unvented cylinder.