Karl Townsend wrote:

I've got a pin hole leak in a copper pipe on my hot water heat sytem.

Murphy is my partner. So, of course, the leak is right where the pipe
goes through the floor and you can't get at it. A proper repair is
going to mean removing the radiator above, cutting out a whole section
of pipe and replacing.

To avoid this job, does anyone suggest some sort of goo to just apply
to the surface of the pipe? Other easy fix?

Karl

Cutting out a section of pipe and replacing it *is* the easy way to do
it. Once you have some experience soldering plumbing you'll realize this
and just cut and replace the offending section rather that spending 3X
the time trying to band-aid it.

You need to at least partially drain the loop so there is no water in
the area you are working on. Get one of the little fiberglass heat
shield cloth squares to use to back the work area and avoid torching the
wall, floor, etc. Have a damp rag available to wipe excess solder from
hot joints for neatness. A pair of channel-lock type pliers is essential
if you try to un-solder any existing connections.

They make couplers that do not have the center dimples / grove and allow
you to slide them fully onto a piece of pipe before aligning with
another pipe and sliding over the joint. Make a mark on the pipe so you
will know when the coupler is centered. A good lead-free paste flux and
some abrasive cloth are essential in getting a good joint, especially on
existing pipe. Use lead-free solder as well, likely all you'll find
these days anyway.

Don't skimp on pipe cutters, get something decent like Rigid and in both
full-size and the mini ones which you can use in close quarters. One of
the mini-hacksaw handles is also helpful for areas too tight for even
the mini tubing cutters. Don't bother trying to use a propane torch,
only use MAPP or MAPP equivalent and use a good trigger-start torch like
a Bernz-o-Matic TS4000. Don't be tempted to use oxy-acetylene, it's too
hot for soldering (good for brazing), plumbers sometimes use
air-acetylene, but not O/A generally.

Use only type L pipe, not the thinner type M. If you have a pinhole leak
and it's not from mechanical rubbing damage, you may well have a lot
more places ready to go unless you are lucky and it's a manufacturing
defect in one spot. BTW, it's a "hydronic" heating system.