Desoldering/desweating

One of those things that you would think would be simple enough:

Am disassembling an external relief line off of a water heater, which is all sweated copper except for the one fitting that's threaded into the T&P relief valve. That fitting can't be backed out because the geometry of the rest of the piping prevents it from being turned.

Normally I would have just cut the pipe, no worries. But I had some time on my hands, and the curiosity bug bit. I've desoldered electrical connections before, but never a sweated plumbing connection.

I assumed that if I just put some moderate separating tension on the pipe, and hit one of the sweated joints with adequate heat for a short time, that it would reflow the solder and the joint would simply pull apart.

Tried it with the old propane torch. No dice. Zero sign of softening or liquefaction of the external solder, even. Hmmmm. It's relatively recent work, thus silver solder, let's try the MAPP torch instead. Tried that. No joy.

Am I missing something obvious here? Any tips or tricks would be much appreciated. Again, this is not a situation where it must be done this way: I can resort to the blade easily. Am just curious as to why this method does not seem to be working as I would have expected it to.

--

If the intial soldering job was done badly where the solder didn't go all the way around, it will bind as you try to pull it apart. Sometimes tapping it with a hammer as your heating up helps.

Hopefully the T&P valve is not leaking any water as you are trying to desweat the fitting , Any water in that pipe and you will be there all day trying to get it off

I bet it's water.

Like Krow mentioned, it maybe water or steam in the pipes. I’ve found out that when you are trying to dismantle copper pipe, (even using mapp gas), and when the pipe won’t turn or come apart, that water of stem is present. When after heating with no luck, pull the flame away, and squirt the pipe with a small amount of water out of a spray bottle. If the pipe doesn’t sizzle, (like water in a frying pan) then you probably do have water in the pipes.

joint

If there is no water in the joint what you are doing should disconnect the pipe, since that is how we do it every day. Even if it is brand new, it is not silver soldered, although it is probably silver bearing solder which is a different thing altogether. However, if there is water in the pipe, then you have a different problem, because that pipe MUST be installed so it drains completely anytime water enters it from the T&P valve.