What size is this rad/valve connection? picture included

[Best]

So...are we any closer to getting a definitive size for this union. I'm leaning to it being 3/4 bsp. The trv is deffo 1/2 and the union is deffo bigger than 1/2 as I've tried a 1/2 nut against it and it's way smaller. I can't see it being metric size, what with the trv being imperial. Anyone agreeing with me on this??

That's what I am thinking. Try a washing machine hose on the valve to see it same threads.
One way to seal the valve is to screw the tail out of the radiator and seal the 1/2" end with blanking plug and then tighten it onto the valve. Have to redo the 1/2" joint with ptfe for into rad later though

 

[Last Plumber]

So...are we any closer to getting a definitive size for this union. I'm leaning to it being 3/4 bsp. The trv is deffo 1/2 and the union is deffo bigger than 1/2 as I've tried a 1/2 nut against it and it's way smaller. I can't see it being metric size, what with the trv being imperial. Anyone agreeing with me on this??

It's not 3/4".
If you are taking the rad off for decor, do what I said with the 5p

 

[StuartP]

It's not 3/4".
If you are taking the rad off for decor, do what I said with the 5p

I get what you're saying with the 5p and tap washer but the nut does not slide of the rad tail, I know this because I had the rad off to remove the wallpaper. This was only a few minutes so no need to blank the valve, I have plasterer coming Monday so will need this rad of for a good few days so want to blank off so can run the CH

 

[Last Plumber]

That's what I am thinking. Try a washing machine hose on the valve to see it same threads.
One way to seal the valve is to screw the tail out of the radiator and seal the 1/2" end with blanking plug and then tighten it onto the valve. Have to redo the 1/2" joint with ptfe for into rad later though

I have been thinking !!!!
Do you mean the type that was a proper union with a half inch tail but 3/4" nut?
I think you may well be right, I had forgotten those.

 

[Last Plumber]

I get what you're saying with the 5p and tap washer but the nut does not slide of the rad tail, I know this because I had the rad off to remove the wallpaper. This was only a few minutes so no need to blank the valve, I have plasterer coming Monday so will need this rad of for a good few days so want to blank off so can run the CH

I think Best may be right with this. There was a 3/4" nut on a half inch tail but it must be 30 years ago.
If it is that then the photo is very deceptive indeed.

You will need a 3/4" blank or washing machine blank from somewhere like wicks.
Failing that, you would need to get the tail out and take the nut off the narrow end and use a piece of lead or a 10p and 3/4" washer.

Whatever you do you need to avoid damaging the face.

I'm starting to think new rad valve would be easier.

 

[StuartP]

I think Best may be right with this. There was a 3/4" nut on a half inch tail but it must be 30 years ago.
If it is that then the photo is very deceptive indeed.

You will need a 3/4" blank or washing machine blank from somewhere like wicks.
Failing that, you would need to get the tail out and take the nut off the narrow end and use a piece of lead or a 10p and 3/4" washer.

Whatever you do you need to avoid damaging the face.

I'm starting to think new rad valve would be easier.

Apologies if the pic was a deceptive. This system was here when we moved in, 30yrs ago so may well be the type you're thinking of. I'm going with 3/4 I really can't see it being anything else. New valve might well be where I end up, but at the moment I just need to get this valve blanked of.

 

[Best]

I have been thinking !!!!
Do you mean the type that was a proper union with a half inch tail but 3/4" nut?
I think you may well be right, I had forgotten those.

Yes, the union with 3/4" nut.
The OP should just get 3/4" blanking plugs as you said, or do what I suggested.

 

[Best]

Apologies if the pic was a deceptive. This system was here when we moved in, 30yrs ago so may well be the type you're thinking of. I'm going with 3/4 I really can't see it being anything else. New valve might well be where I end up, but at the moment I just need to get this valve blanked of.

3/4" blanking plugs probably will do your job.
Try B&Q or Screwfix.
If you are going to replace the valves shortly, then just get those tails screwed out of radiator and have them blanked off with your 1/2" blanking plugs

 

[StuartP]

3/4" blanking plugs probably will do your job.
Try B&Q or Screwfix.
If you are going to replace the valves shortly, then just get those tails screwed out of radiator and have them blanked off with your 1/2" blanking plugs

Thanks Best, I'm going with 3/4, picking some from my local plumbers merchant tomorrow.