The metal pipe that comes out of the wall and feeds water into the cistern on my toilet is connected to the plastic cistern pipe (inlet valve pipe?) by a service valve. It is pretty much identical to this one:
There is a leak in the connection between the female end of the service valve and the threaded plastic pipe to the cistern. The leak stops if I turn off the valve (so at least that's something) but starts again as soon as I turn it back on. Not a serious leak, just a drip, but it drips about a litre in 12 hours so without a big bucket under it, if I leave it on it will flood my bathroom while I'm at work.
I figured it was the washer that had gone, so I bought a pack of these:
I took the washer from the service valve to the shop when I bought them and compared them, so I got the exact same ones (or at least they look and feel identical). I have now tried every combination I can think of, and haven't been able to stop it from leaking. I have tried with a single washer, with two washers together, I have wrapped PTFE tape around the thread on the plastic pipe, I have even tried a washer wrapped in PTFE tape, but nothing seems to help.
My question is: - Is it worth replacing the whole valve? Could there be something wrong with the valve that isn't just the washer? The valve part works fine, because the leak stops when I turn it off. I did notice when I took the old washer out that there seemed to be tiny chips of what felt like concrete or something in there, not sure what that is or where it came from. - Could there be something wrong with the thread on the plastic pipe, or is this unlikely to be the issue? - Is it worth trying a rubber washer instead of the fibre one that was in there already? - Should I be tightening the valve onto the pipe really super hard, or should a few turns be enough if the washer is doing its job?
I have done a few bits of pieces of DIY before but I have not done much plumbing, so any suggestions would be welcome!