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joshm

Hi all,

I've come to the forum to ask for some advice about retro-fitting TRVs to all the rads in my house. I'm confused about fitments since when I went to buy the valves, they seemed to come in an odd size when compared to what I have at the moment.

I am pretty sure that my heating uses standard 15mm pipework. The confusing part is how I am supposed to mate a TRV with the rad itself. Now, as I understand it, most UK rads take a 1/2" BSP thread. But it seemed to me that my rads had larger threads? I know of the existence of 3/4" BSP in older rads, but I'm unsure whether my rads are considered "old"?

I've attached a few photos of the type of thing I have at the moment in the hope that someone can point me in the right direction. Although caked with old paint, the diameter of the inlet pipes (from valve to rad) seem to be about 3/4" so it would seem to me that that's what I've got.

If that's the case, then how do I go about fitting these TRVs? Is there a converter/adapter I can use to replace the existing adapter? And would the use of such things result in me needing to move the 15mm feed pipe from the heating circuit? I'm keen to make the change and am a pretty able DIY-er, I but don't fancy it turning into some huge project involving blow-torches and pipe cutters!

Thanks for any advice you can give!

Josh
 

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you can get 3/4 x 1/2 bushes from industrial pipework stockists
 
Forget 3/4 x 1/2 bushes - they are for a different task - I think the previous poster has got confused.

You need to take the radiator tails out and replace with the 15mm ones which come with the TRVs.

You need a radiator key (bit like an oversized allen key) which you use to remove the old tails. Put the new tails in with hemp and Boss White. You may find the nut onto the copper pipe has a different thread pitch so you will need to remove the olives and change the nuts if this is the case. If you have a lot to do it may be worth investing in an olive splitter to speed things up.

I would replace the lockshields as well as they will be knackered by now. The easiest thing to do is get several packs of the Cosmos radiator valves from Screwfix (they are really cheap) as they have the 3/4" threads on them which will save a lot of efort as it means you won't have to remove the existing tails on the lockshield end of the radiators. Put some Boss White on the olives and the dome faces of the old tails to ensure good fitting of the old joints.

For the valve type in the second picture, you need a valve with a 1/2" female fitting in the bottom as opposed to 15mm compression. Screw up with hemp and Boss White. When you undo the old one / tighten up, you need to use a spanner on the valve and also on the nut below the valve or you may kink the pipe.

BTW have you not considered replacing your radiators for some nice new ones as yours look old and covered in paint (which reduces efficiency).

Whatever you do, don't forget to add inhibitor to the sysem when you refill.
 
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The pics u posted are standard half inch bsp. Remove the whole valve Inc the nut and olive on the 15mm pipework(u may have to hacksaw the olives off). Tape(ptfe) up the threaded straight part of the trv and screw into the radiator Then fit the rest of the valve, quite simple but if in doubt get sum1 who knows what they're doing especially if you've got an open vented system-they are easy to drain but can be a complete nightmare to refill with the possibilty of airlocks and choked cold feeds (dependent on water quality and age)
 
The valve in the second picture is not a compression fitting with olive onto the 15mm pipe but a female connection threaded to the valve. You need to replace with a TRV with a 1/2" female fitting as opposed to 15mm compression.
 
I'm viewing on the iPhone so I won't argue that point with u. (the more I zoom in on the pic the more blurred it becomes). But to me they both looked 15mm compression nuts and I'd be quite surprised if was anything else. The config u speak of is very unusual round my way, even on older systems. But as I say it's difficult to tell without seeing it properly
 
The valve in the second picture is defnintely NOT fastened with a compression nut!
 
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