How to replace old 3/4 Radiator valves with 15mm TRV

[newcomma]

Hi There,

I want to swap out my old valves for TRVs but the threads are different sizes, and I'm unsure how to resolve it.

My current existing radiator valve setup is:

The current valve has a 3/4" thread going to the radiator. I can't quite work out what's on the radiator side, but the compression nut seems 'attached' to the radiator (i.e. can't pull off of the metal it's on).

The pipe side is compatible with the new TRVs so no issues there.

I'm not sure what I can do to adapt the original 3/4" compression nut to the new 15mm thread on the new TRV

I've had a look at a few 3/4" to 15mm 'adapters' of various sorts, as well as bush's but I don't think any of them can help. With the bush as an example, ignoring the fact I can't find a 3/4 to 15 online, it would be threaded without a compression, so I'd need to just screw the TRV into it, which doesn't seem doable.

I'd really appreciate any advice/links on parts I need, or if a more serious adaption is required.

I'm really at a loss! I was hoping it'd be an easy problem to solve but it seems like old radiators are not common enough to fill nearby plumbing parts shops with the help I need

 

[PETE 123]

You will have to unscrew the tail in rad with a special tool.

 

[newcomma]

Thanks Pete, what tool is needed for this? And what do I then replace it with?

 

[ShaunCorbs]

Multi Size Radiator Key & Ratchet

For speedy assembly of most valve tails to radiators.

www.toolstation.com

Replace with the one that came with your trv with ptfe tape

 

[newcomma]

Hi Shaun, thanks for the link to the tool to remove the tail.

But I'm not sure what your comment implies, sorry for missing the obvious

Are you suggesting doing:

1. aRemove radiator tail, I'm left with a 3/4" thread on the inside of the radiator where the tail used to screw in?
2. Take off the compression nut from the TRV
3. Wrap the 15mm male thread on the TRV with enough PTFE tape to widen it so it'll fit into the 3/4" thread in the rad?
4. Screw the TRV directly into the radiator thread

If I've understood that all correctly...

As the TRV is solid metal, if I screw the whole TRV into the radiator, the TRV itself will need to be turning, but I also need to align it vertically to match the pipe connection, and I'm worried I can't both make it completely tight, and align it correctly?

If I've not understood something please shout!

 

[newcomma]

Ah I'm now looking at the parts which came with the TRV,

Are the two bits in the middle the new Tails? Will they definitely fit the old radiator?

I don't quite understand how the compression nuts then attach the TRV to the new tails, the non-threaded side is smooth metal, the nut fits over it. So long as I tighten the compression nut enough it'll "just work"?

 

[ShaunCorbs]

The rad will be 1/2 yes there the tails eg shaft with threads one end

22 turns of ptfe on the threads (u tube it if you don’t know how to apply it as there’s a way / nack)

Grab a spanner to fit on the hex / flats screw into the rad until one threads showing/ it’s ft

And yes the compression nut will grab onto the shaft 1/2 - 3/4 of a turn of the nut approx

 

[newcomma]

The rad will be 1/2 yes there the tails eg shaft with threads one end

22 turns of ptfe on the threads (u tube it if you don’t know how to apply it as there’s a way / nack)

Grab a spanner to fit on the hex / flats screw into the rad until one threads showing/ it’s ft

And yes the compression nut will grab onto the shaft 1/2 - 3/4 of a turn of the nut approx

Amazing thank you for detail, going to drain the system and give this a shot tomorrow, will update again / shout for more help

 

[newcomma]

Followed your instructions @Shaun and it went perfectly.

Spent the day draining, replacing 7 old valves with the TRVs (The ratchet radiator key was a godsend for easily taking off the tails), fitted everything back together, sorted inhibiter, tightened up the few minor leaks and everything seems to be working perfectly.

Not without its own problems of course, one of my radiators has an older bleed valve so had to hunt around for some clock keys to fit - but I've become a lot more confident in being able to do something like this myself again in the last 24 hours - and get a general understanding of how it all fits together.

Thanks so much for taking the time to help!

 

[Daley power]

I have a 3/4" rad system i'm working on. Was hunting a potential trv to replace the broken one when i stumbled across this site, they do exist, it's probably 20 to 30 years old. 3/4" top feed rad to 22mm tail to trv to 15mm feed. Obviously industry standards have made this obsolete so a new rad will have to be fitted.