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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!).
No. "Teflon tape" is used on the threads of joints, not to seal leaks outside of joints. It's not adhesive like tape, so it wouldn't stick to the outside of the pipe at all.
If you don't know what you're doing, I'd bring in someone who does. Based on the amount of corrosion, it looks like it's been leaking for some time. It could be as simple as tightening the nut, or it might require disassembly and reassembly (possibly with new parts).
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.
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. 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.
The fitting must be disassembled, cleaned and then apply teflon pipe dope to the threads and tighten snug. Once snug turn 3/4 turn and stop. Over tightening compression fittings will damage the collar under the nut and the pipe. If this does not work the pipe and collar may be damaged and need to be replaced.
Your first answer from Been There is the correct action. Shut off your water, undo the fitting, clean off corrosion, apply Teflon pipe dope to threads and retighten. If you still have a leak and have some pipe to work with, cut off the compression ring on the end and install a new compression ring and do the same.
You should first turn the water off at the main. ( where the meter is located, usually in the front by the curb) Have a bucket close by to catch what water is left in the pipe. You should be able to turn the bolt just above the corrosion to the left and loosen the connection. Pliers may be needed if it hasn't been loosened in a while. After loosening, it should disconnect enough where you can maneuver the pipe out from under the bolt. Take a look at the pipes condition. If it's threads are still visible and the pipe is still in good shape with the corrosive material mainly where the dripping is on the outside, then u can apply a layer of plumbers tape around the threading and reconnect. The tape otherwise will have no affect on the leak without taking these steps. If the leak continues or the pipe is deteriorating, then disconnecting both ends of the pipe and taking a trip to Home Depot will probably be necessary.
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.
