Fitting TRVs

This bit is a stupid question isn't it. It must be either 3/4 or 1/2" because why would anyone bother setting up for anything else.

I think you have missed the point of the question by snipping and only replying to one bit (missing the 'bigger picture' in the process).

It wasn't the diameter of the input pipe, it was the distance between that pipe and the radiator, something someone replacing a std with a complete new TRV would like to know.

Cheers, T i m

Not quite, because I replied to my own question!

I was referring to the size of thread that connects the valve to the tail, and realised that surely no one would make it anything other than 3/4 or 1/2, so if it looks like a 1/2, it is a 1/2.

it was the distance between

That question stands.

Not all makes of TRVs are the same or indeed interchangeable. So you need to look for ones which are a direct replacement.

You've rather obviously never done this job. The centres of the pipe and rad can be different between a LSV and TRV, as can the length of the pipe. Even the type of olive used different.

Doh! ;-)

Well, I'm not sure you can even assume they will be interchangeable, even if they are nominally the same size / type of fitting.

I say that because I have gone to replace say a gate valve and hoped to retain the existing nuts / olives, only to find the thread a different pitch / tightness?

I think has been answered elsewhere. I think with my experience with plumbing, unless you are replacing exact like for like, there is a good chance that something will be different (and rarely in your favour). ;-(

Cheers, T i m

Before anyone else jumps in - I retract my assertion that the question (which I asked) is stupid.

As noted elsewhere, I asked the question.

Damn. I have actually done it before (and had to change the tails), but everything looked a bit more standard this time. If I have to change everything I guess I'll give it all a flush too.

You may get away with it if the physical size of the valves (inlet to outlet) match.

When I replace all my 20 year old TRV I had to change the tails in the radiator. The valve body on the old TRV was longer. In addition I found the screw thread on the compression nut on the old fitting did not match that on the new fitting necessitating removing the olive in order to fit the new nut. On many pipes removing the old olive was difficult and I found it easier to cut the old pipe and solder in a new piece. The exercise was complicated by the pipes having been painted and having to syphon any water out of the existing pipe(s) before soldering.

For the tails I already had

That tool looks like a vast improvement on the radiator spanner I used last time. I used a radiator spanner and ended up having to hit it with a hammer to get it to shift.

As I was living in a flat, and doing the work in evenings, I did that particular job on bonfire night to minimise disturbance to everyone else.

Photo might help as I think there's a British Standard for radiator tails so there's a fair chance you'll be OK - /if/ (a) you start off with ones that conform and (b) know the pipe size/material and angle.

The ratchet handle is the same as you get with a 1/2 inch socket set for a car etc. so if you already have this maybe the stepped socket can be purchased separately. I don't know if the Screwfix is the same as mine as the one I have also has deep grooves in two faces of the hex steps to suite the fittings that have two internal lugs. This is shown in

Well its not as daft as it sounds...

The tail socket into the rad is almost always 1/2" BSP female. However the other end of the tail varies. Traditionally it was a cone fitting retained by a 3/4" BSP nut that was captive on the tail. However more commonly these days the tail is often just a length of 15 mm pipe, and the valve has a 15mm compression fitting that then connects to that (ultimately leaving a 1/2" BSP not captive on the tail, but retained by the olive rather than the cone fitting).

Ahem, pl. replace" tails" by "valves".

My original TRVs, shed own brand, had an 'olive' which fitted to the end of the copper pipe, rather than the usual types which fits over it. And when replacement time came, couldn't find the same design.

But I'd only buy Drayton now. Saving a few pennies isn't worth it in the long run.

I would have thought that the chances are minimal. The job will be easier if there is a section of pipe that is horizontal below the level of the radiator bottom.

I prefer to use a programmable thermostat as these allow the temperature to be automatically varied through out the day. I had a similar problem when I removed some old TRVs some of which were leaking.

Definitely do not assume standard threads, you may have to remove the fitting that goes into the radiator, rather than just swapping the "valve" bit. This needs a big allen key and they are sometimes very tight from corrosion. In my experience you can usually get away with the slightly different dimensions by using the flexibility of the copper pipes, provided they are not too constrained close to the radiator. One of those jobs that usually takes longer than expected, IME.

Faced with removing old olives, no chance of a tool and pipes up from concrete floors, I found that a junior hacksaw, cutting diagonally across the olive so that it didn't damage the pipe, worked well. Cut the slot to within a gnat's of the pipe - it'll probably spring open for a v. short way as it gets weaker - then screwdriver finishes the job.

Some of the modern ones seem to use a couple of flats on the stem to allow them to be turned with a spanner, rather than having the hex inner profile... Personally I prefer the hex versions.

Yup, although sometimes you get lucky...