Unvented Hot water cylinder instalation

3 Mar 2010
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United Kingdom
Hi all,
I am about to remove the old copper hot water cylinder and install an unvented steel hot cylinder in order to provide hot water to the whole house ( a two bedroom house with one bathroom)
A friend of mine is going to do the plumbing, but I am unsure about the electrics. Am I allow to do it myself? Am I right to assume that I can connect to the same socket where the old cylinder is? If so which one as the old cylinder has got two sockets one for the bottom immersion heater and one for the top immersion heater.
What is the best cylinder size (litres) for this size of house?
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Cylinder size is determined by number living there and bath/shower usage.

Only a qualified person is meant to install plumbing and electrics on an unvented cylinder. Although as far as I can see anyone can fit them as long as they are checked and commissioned by a qualified person.

If you are asking such basic questions about electrics then I don't think you should be doing it without professional guidance on site!

I would say be dead careful. I am handy around the house, like really handy, do pretty much all jobs myself including complex jobs. However, I have just had a beautiful brand new 210 litre unvented tank fitted to my loft by a professional Heating Engineer. I decided not to take this on as if you get things wrong with one of these chaps, especially the wiring you could have a potential bomb in the loft!

If you get things really wrong, the worse case scenario is that Water can turn to steam, then Saturated Steam, expand the gases by significant amount and..... 'BANG'. :(

I once got told on this forum, there is a big difference between something that appears to be working correct and actually working correct.

This was one job I decided to not do myself for this reason, be careful!
Interesting....OK I am a bit like you, and like to fix everything myself but i agree I should not touch this.... this time.
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An unvented cylinder with superheated water creates 500 times the volume when it explodes.

That's why they demolish buildings!

That's right Dan.

Its actually widely quoted as expanding by 1700 times!

Quite enough to blow up most houses.

Widely quoted at 1700 times but not something easily measured.

Not very important either.

Just a vast increase causing a very powerful explosion!

I did not expect quiet so many responses on this subject! I have reviewed the reply's with great interest and even viewed the video on You Tube. I am even more glad I had this potential Bomb installed by an expert now.

North - Apologies, don't mean to hijack this post, it's just our circumstances are so similar here.

So North, can we all talk you in to having your installation professionally fitted? If the answer is no, please review the video on You Tube and then think again!!!

P.s - The cylinder I had fitted was a Potterton Gold which get great reviews and work out reasonble for the money. I forget, but something silly like a 25 year guarantee is not to be ruled out too quickly either!

Have fun....
I already have contacted a couple of engineers from check a trade for a quote, so the idea to do it myself has vanished. Now the question is what would be the cheapest option for a 120 liters tank?Can I assume the same as for most white goods that cheap makes ar as good as overpriced well known makes?.
And also where is the best place to find a reliable engineer? I do not trust check a trade too much but where else can i find one that it can prove reliable? That is which website publishes real reviews if there is any?One of the reasons I like to do plumbing, electrics etc myself is not so much for the enjoyment and the economy but also for the destruction that some tradesman have left in my life in the past.

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