Question: [![enter image description here](https://i.stack.imgur.com/1gO9Z.jpg)](https://i.stack.imgur.com/1gO9Z.jpg)

Hi there, 

This is some piping to my Saxon hot water system. Just above where the white/green corrosion is is where the leak is.

My question is, can I use plumbers tape on the outside of this to seal the leak? 

I do not want to pull it apart as I don't know what I am doing. I am basically after a quick fix and thought plumbers tape (teflon tape) would suffice. If not are there any other options? (other than the obvious in getting a plumber out (again!).

Answer: 
Wrapping externally with teflon tape wouldn't help. Teflon™ doesn't stick to **anything**; the only reason it works when used properly (wrapped on threads before assembly) is that it's squeezed tightly between the external and internal threads (using Teflon reduces friction so the joint can still be fully tightened).

The leak is at a [compression fitting](http://www.naturalhandyman.com/iip/infplumb/infcomp.html). The real way to fix this would be to disassemble, clean the nut and seat, trim the last 1" from the end of the copper pipe, install a new ring, and then reassemble the joint. If you can't disassemble it, then you might get away with cleaning off the corrosion with a wire brush and applying some sort of caulk or glue (perhaps an epoxy), but especially as the joint is hot it will be tough to find something that will last.
You cannot repair this externally with tape, but soldering is not necessary either. Simpler than learning how to properly solder (sweat) fittings together, look into "Shark-Bite" style fittings. These are more costly than soldered fittings but are very simple to install and require no tools. They simply press onto the (clean) ends of a pipe. Depending on the condition of the pipe hiding under the fittings in your photo, you may need to clean it up with sandpaper, or if that is a flared fitting, even cut it off squarely first with a tubing cutter (NOT a hacksaw). I'll let you google for a how-to on shark-bites rather than rambling on here myself.

Side note: You will encounter two types of threaded plumbing fittings. Old school iron pipe has tapered threads which become increasingly tighter as the pieces are threaded together. This is where teflon tape is used, to fill any irregularities between the male and female threads of the pieces being joined. Back in the day, before teflon tape became available, "pipe dope" sealant was used. Other fitting types use straight, non-tapered threads to simply pull together two pieces tightly together so that they seal, possibly with a gasket, or a flared end against a mating conical surface, or by compressing a compression ring of soft material (typically copper). Do not use tape on these, it serves no purpose and just gets in the way. The nut shown indicates that the fitting in your photo is a compression fitting (uses straight threads), but without taking it apart we can't see whether it uses a compression ring or a flare.