I recently replaced an old, leaky shut-off valve with a compression shut-off valve. I cut off the copper pipe cleanly and made sure the end was clean and burr free. After tightening the nut as instructed, I still had a leak from where the valve connects to the stub. I've adjusted it a couple of times and added teflon tape to the threaded portion of the valve. The leak is now very minimal, but still exists. Any suggestions? As I have a second one to replace, I want to get this correct. Thanks.

Taping the threads on a compression nut won't stop anything as it isn't the threads that hold water it's the ferrule,(see image). You do have a ferrule installed don't you? If so, then crank down a little harder. If not then the compression goes on the pipe first then the ferrule and finally the anglestop. Good luck, Tom

Thanks so much for the help. So the teflon tape is pointless in this situation? Being very simple-minded about plumbing, I just always use it. Also, I learned a new word, ferrule. I did use the ferrule but didn't know what it was called.