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: 
Your other option is to ditch compression fittings and **learn how to sweat** (solder) copper pipe. Or if you do have a plumber come out, have them replace every accessible compression fitting with sweat fittings that will never leak ever again.

Compression fittings are prone to leakage, even when they aren't eating away your pipes with galvanic action, as you can see they are, with the black patina on that old stub.

I'm pretty sure **Stack Exchange can help you** with every aspect of learning how to solder, and if you're willing to do the work, the cost of the tools and materials will probably be less than a service call, and then you'd have the tools and the talent for work in the future. Having one easy elbow to sweat is a great place to start.

If you know anyone who knows how to sweat pipe, they should be able to show you how, *and* you'd be done, in under an hour: for the cost of a torch, solder, flux, fittings, a piece of sandpaper and a six pack of beer.
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.