Can't screw backnut to the lockshield valve

[learninghowto]

Hello all. I am trying to install a radiator and I am stuck in the last step. So, for whatever reason, I can't tighten the backnut with the olive nut and the lockshield valve. I can't figure out why this is happening. Any thoughts? Thanks in advance!

 

[terryplumb]

You are trying to connect a rad tail to a rad tail extension. Totally wrong.
If you change the radiator valve to one with a 15 mm compression fitting ( rather than 3/4 inch union) you might have a chance ,but the rad tail extension may be too short to reach ,and you may need a longer one.

 

[learninghowto]

Hello Terry and thanks for your answer.

Could you help me understand it a bit more? So to mind, I bought that lockshield valve

Radiators | Screwfix

Buy Radiator at Screwfix.com. Huge range of styles, materials & sizes. Energy efficient. Residential or Comercial. Top Brands. Delivery or C&C available.

www.screwfix.com

Isn't it what goes on the opposite side of a TRV valve?

And because the radiator is
narrower than the old one, I bought this rad tail valve extension

Made4Trade Rigid Radiator Valve Extension 1/2" x 15mm

A rigid extension piece that can be cut using a pipe cutter to get the exact length required when installing a radiator.

www.toolstation.com

I thought that the rad tail extension is the same as a rad tail valve but just longer..

So, the lockshield valve is 1/2", the backnut is 1/2" so I thought they will fit.

P.S. On the other side, where I used the same rad tail extension, the backnut went in smoothly.

Please help me understand where I am wrong mate...

 

[terryplumb]

Your valve is a 3/4 union to its tail which is 1/2 in

 

[learninghowto]

Fair enough.. So the valve is 3/4" even though in Screwfix's website it says 1/2"... Can't understand how you can miss the description on something simple like this one... Anyway, thanks for your help.

 

[terryplumb]

The part that screws into the rad (the tail) is ¹/² inch thread. But the union that connects the valve body to the tail is 3/4 inch union.
Your TRV had a ¹/² inch tail ,but the tail connects to the TRV body with a 15mm compression fitting.
If you had a lockshield valve with a 15 mm compression fitting to its tail ,that would connect to your tail extension. ( If its long enough to reach)

 

[Elkato531]

A bit of a bodge, but given where you've got to, you could use a female iron fitting between the locksheild valve and the rad tail. It will look like a diy fudge but the connections will match up and you should be able to get it to seal. You will need to cut the rad tail a bit shorter to fit.

Made4Trade Compression Coupler Female Chrome Plated

• The only compression fittings range manufactured in the UK• Create a mechanical heat free connection• WRAS Approved• Suitable for use on both gas and water• Suitable for Domestic and Commercial Heating and Plumbing Applications• 25 Year Warranty • Manufactured to EN1254

www.toolstation.com

 

[Madrab]

Buy one of these and replace the one you fitted with it

https://www.screwfix.com/p/drayton-white-angled-lockshield-15mm-x/7877g

Your rad tail extension might not be long enough though.

 

[Madrab]

Oh and don't use PTFE tape on the thread of a compression joint, it performs no function. If you have a need to use it anywhere, then it only goes around the olive.