Leaking soldered joint on copper pipe

Just a quick(!) question, why would a weeping soldered fitting continue to weep at the same rate when the supply is turned off and the pressure removed (by opening a tap) ?
Is this just a "They all do that" thing?
...
Background if interested, this is a soldered "T" in an inaccessible place (aren't they always?) and it's currently weeping at about 1 drop an hour. I'm worried that could worsen, possibly without further warning.
The weep is coming from a "carbuncle" on the fitting itself, I'm guessing it's a flux residue problem.
Getting to it is not going to be easy, barely got enough access to see it, the current preferred plan is to just run another pipe and nix the bath tap that the other end of this one is connected to. Never use that tap anyway (because shower) and there is a refit in the budget at some point :) :)
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It can't leak water if there's none in the pipes. ;-)
But running a tap isn't guaranteed to empty the pipes completely. As you'll find if attempting to solder ones which have been in use.
I tend to blow them through with a compressed air supply before attempting a repair.

You need quite a bit of space to dismantle a soldered joint and re-make properly. But then you do with a compression fitting too.

I've seen brand new fittings with a pin hole in them. Before just how well soldered it was comes into it.

Could you cut the pipes in a more accessible place and perhaps pre-fabricate the T including pipe ends? Then used end feed couplers?
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On 01/03/2018 13:32, Dave Plowman (News) wrote:

You said it was dripping at 1 drop per hour. So capillary action is possibly more important than pressure.

I used a wet and dry vacuum cleaner recently. It worked a treat.

Push fit might be a lot easier in a confined space.
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On 01/03/2018 13:48, GB wrote:
<Big Snip>

That's the current plan...
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On 01/03/2018 13:32, Dave Plowman (News) wrote:

Indeed :) I was just surprised a change of pressure didn't change the amount. But probably it is capillary action then, as GB notes.
<Snip> > Could you cut the pipes in a more accessible place and perhaps

Not unless I either change size considerably or pull the bath out, which would necessitate a fair degree of destruction due to the way it's been installed. Fortunately access to the shower pipes is a little more straightforward so an alternate pipe route looks favourable.
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On Thu, 1 Mar 2018 12:33:01 +0000, Lee wrote:

If there is any water left above the weep the weep is still under presure from the weight of that water.

Or faulty fitting? A "temporary" fix for something that slow would be to bind it with self amalgamting tape.
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On 01/03/2018 13:49, Dave Liquorice wrote:

I have some of that, but to be fair if I had the access to do that it wouldn't be too much harder to remake the fitting :)
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On Thursday, March 1, 2018 at 1:49:37 PM UTC, Dave Liquorice wrote:

... and so turning off the tap might actually result in the leak stopping.
Robert
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On Thursday, 1 March 2018 14:21:36 UTC, snipped-for-privacy@gmail.com wrote:

ue

re

.
How easy is it to get a blow torch to it? During some building work I was h aving done, the builder knocked a pipe which was below any drain off possib ilities. A soldered joint started leaking so I ended up getting 2 blow tor ches to it and eventually was able to get it hot enough to melt the solder (having added flux first) and fix the joint. From memory (it was a good fe w years ago!) I *think* I ended up draining what I could first so assume th e blow torches effectively evaporated the water enough to get hot enough fo r the solder to flow in.
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On 01/03/18 15:54, snipped-for-privacy@yahoo.co.uk wrote:

BTDTGTTS but it can take an awful lot of propane
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On 01/03/2018 15:58, The Natural Philosopher wrote:

A better option than this or tape would be the special epoxy putty made for plumbers. I had a somewhat larger drip from a hot water cylinder once and used this for a "temporary" repair which in fact lasted years before I changed the cylinder for other reasons. You can apply this on to wet surfaces. I didn't even drain the cylinder, so it had a pressure of about 6 foot head (i.e. 0.2 bar or 3 psi, much less than mains water pressure, but if you have the mains off and the tap open for the hour or so it takes to set, you should be OK.
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Thing with soldering a pipe which has water in it is even if you do get it hot enough, there's a chance the steam generated will stop the solder joint being made properly.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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On Thu, 1 Mar 2018 12:33:01 +0000

Are you sure it's a leak and not condensation?
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