Will cast iron radiators work on 8mm microbore system

21 May 2012
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United Kingdom
Hi all.

I am fairly confident with D.I.Y. but pretty much a novice when it comes to plumbing. I am planning to plumb in 3 new cast iron radiators but on a bit of a budget. So I am hoping to do the work myself.

I already have a central heating system in place, it is already run on 8mm micro-bore pipework. I live in a ground floor flat with 5 steel radiators in place. I am hoping to remove 3 of these steel radiators and pretty much replace with 3 of the new cast iron ones. I am confident at connecting new valves to fit the existing pipework.

The cast iron radiators are larger than my steel ones to be removed.

The new cast iron radiators are traditional 4 column sizes below
760 by 950 2.17kw 7410 BTU 15 sections
660 by 950 1.74kw 5952 BTU 15 sections
660 by 950 1.74kw 5952 BTU 15 sections

The boiler I have is a Worcester 28i, seems to be in good working order.

-Will the cast iron radiators work on my existing 8mm micro-bore pipe? As i didn't want to change the pipework.

-Will my boiler work with the cast iron radiators?

-How do I tell if I have a pump and how do I know if my pump is good enough to pump the water around the system?

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well i wouldnt do it in my house. if it did work, it wouldnt be for very long.

why the budget? all spent up on the cast iron rads?
The pump is part of the boiler so there's not much you can change about that.

Those rads will need a higher flow rate than the 8mm pipe can provide, I'm sure they'll work but I doubt they'll get as hot as they should.

Basically, they'll dissipate heat quicker than they're receiving it.

By all means do it but you may not get the performance you want.
Hi Andy
Thanks for your advice.

The website selling the radiators recommend that they can be used on the 10mm micro-bore pipe but they are not tried and tested on the 8mm.

If I changed the pipe to a larger size will the cast iron radiators perform better?

What pipe size would you recommend?

I have a Worcester 28i boiler would the pump on there be powerful enough?
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it depends what you mean by better...if the current pipes and radiators put in enough heat bigger radiators will continue to do so, but given the high water content of the radiators you may notice that the radiators are not as hot as the old ones.

This does not mean that they are not working, in fact they will be giving out the same amount of heat but at a lower temperature...it will make for a nicer environment...as there will be less localised over heating...

all other things being equal then the system will continue to perform adequately...
If the 8mm pipe delivered enough heat for each room before, it will afterwards. You haven't changed the heat requirement, although the rads may take a bit longer to heat up from cold. Microbore was OK, it's just out of fashion now.

It will deliver at least as much heat as before.

Careful balancing may be needed to get the best out of it. But 8 mm is largely self balancing!

New c/i rads :eek: I`m fitting old ones @ £25 - £40 each :mrgreen: I collect them on my cart when I`m out totting ;)

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