Chrome compression with plastic

A pipe insert. Wrap the olive with PTFE.

Just make sure you are using the correct pipe support insert, the compression fitting should work no problem. If you have a leak, check for grit on olive or pipe. At a push a slight smear of plumbers mate would fix ... but should not need it.

Pipe supports are not required here. I have copper pipe connected to the 15mm end of the chrome elbow. The other end of the elbow is directly connected to the inlet to the cistern.

I assume the (vertical) cistern inlet is 1/2" bsp and therefore the same size as the 1/2 end of the elbow.

Would a dab of fermox LS-X be ok to use?

Arthur

Are youi sure you have a fibre or rubber washer between the elbow and the spiggot on the cistern valve?

Yup, but you need a tap connector end to the fitting rather than a normal compression end.

It might

PTFE tape more like.

You shouldn't use jointing compound on plastic pipe / fittings - only silicon grease, maybe Vaseline or possibly PTFE tape on the olive (although I have never needed to) and the proper support sleeve in plastic pipe - if it doesn't seal, it must be a dirty joint or possibly a faulty fitting ( I have had that but its very unusual)

Nick

Yes. The chrome isolator elbow has a captive nut which I believe indicates a tap connector.

Arthur

And it has a fibre washer.

Sounds like you are trying to mate a standard 15mm compression to a female bsp theaded inlet ... not correct.

You need a tap connector .. strainght or 90 Degree to suit the layout. This connector has a fibre washer which makes the seal against the end of the threaded inlet.

It might be worth trying a neoprene/plastic washer instead.

Lee

Has the plastic inlet cross threaded? This is very easy to do with a chrome tap connector on a plastic spigot. A cross thread may prevent enough sealing force being applied, or present the surfaces at an angle.

Also, is the end of the plastic perfectly flat? Any nicks or dents can prevent the washer sealing.

Christian.