Replacing TRV on radiator, 15mm pipe to 22mm radiator

Emkakora · Oct 27, 2019

I’m trying to replace my TRV on my radiator but have found that my pipes are 15mm copper but the radiator has a 22mm radiator tail.
There isn’t enough space between the valve and the radiator/pipes to fit a compressor (which is what I think I need...)

the old broken valve looks like it goes from15mm and then to a Sort of “trumpet” shaped 22mm, if that makes sense, but I can’t find any premade 15–>22mm TRVs.

any advice?

ShaunCorbs · Oct 27, 2019

did a tail / a part with another nut on the end come with the new trv ?

as you would replace your existing rad tail with your new one

Emkakora · Oct 27, 2019

ShaunCorbs said:
did a tail / a part with another nut on the end come with the new trv ?

as you would replace your existing rad tail with your new one

It did, and it was 15mm as well. We think the existing tail is painted to the radiator as we couldn’t get it loose, if it could be loosened at all....

I’m mostly curious as it looks like whoever put the original TRV on managed to find one that connects 15mm pipes to a 22mm radiator. Any ideas where I can find a new one?

ShaunCorbs · Oct 27, 2019

it will come out so just need to try more force as there isnt a trv out there that connects to a 3/4 threaded nut only a lockshield

Emkakora · Oct 27, 2019

ShaunCorbs said:
it will come out so just need to try more force as there isnt a trv out there that connects to a 3/4 threaded nut only a lockshield

If we did manage to get out the tail, would the one that came with the 15mm trv fit?

Ric2013 · Oct 27, 2019

The radiator tail will be 1/2" threaded. It may possibly be 3/4" threaded. It won't be 15mm or 22mm as these metric dimension refer to the outside diameter of the copper tube, not the nominal thread size which is related to the nominal bore of steel pipe (and is still measured in inches, even in continental Europe).
The trumpet shaped thing probably has an internal hex that you put a large Allen key-type thing in to unscrew and then you'll probably find the radiator is internally tapped with a 1/2" BSP tapered thread compatible with pretty much all modern tails.

I'm pretty sure you can still get replacement heads for those old Giacomini TRV bodies, if the valve inself is still working, by the way.

Emkakora · Oct 27, 2019

Ric2013 said:
The radiator tail will be 1/2" threaded. It may possibly be 3/4" threaded. It won't be 15mm or 22mm as these metric dimension refer to the outside diameter of the copper tube, not the nominal thread size which is related to the nominal bore of steel pipe (and is still measured in inches, even in continental Europe).
The trumpet shaped thing probably has an internal hex that you put a large Allen key-type thing in to unscrew and then you'll probably find the radiator is internally tapped with a 1/2" BSP tapered thread compatible with pretty much all modern tails.

I'm pretty sure you can still get replacement heads for those old Giacomini TRV bodies, if the valve inself is still working, by the way.

Thanks for all the help, I really appreciate it.

I think the whole valve is broken (I can get the top off but not the collar below).

can I ask a stupid question- how do you know if it’s 1/2 or 3/4” ?

ShaunCorbs · Oct 27, 2019

1/2 will measure around 20-21mm dia

Ric2013 · Oct 27, 2019

The horizontal bit to the right of the large nut (painted white in your case) is what Shaun is referring to as being 20-21mm diameter. Which is probably roughly the same as the thread on your new one. In practice, the thickness of that section is likely to be ish. The critical dimension is the thread that will be mostly hidden inside the radiator, and my guess is it's a bog standard 1/2" British Standard Pipe even though that radiator is quite old.

I think you would cut that lower collar off to remove the head (technically I think you can lift it to release the claws), but only worth doing if plan A gets too complicated and your budget doesn't stretch to a plumber. I have a friend with a large number of Giacomini valves and seem to replace one every year and free off another mid-season. He's too tight to want me to change the lot in one go

steadyon · Oct 28, 2019

Have a look on the internet for union TRVs. They are more expensive than ordinary TRVs, but should fit directly to the existing tail coming from your radiator. Alternatively, as suggested above, change the radiator tail.

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Replacing TRV on radiator, 15mm pipe to 22mm radiator

Emkakora

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ShaunCorbs

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Emkakora

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Ric2013

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Emkakora

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