Soldered joint failure

[endecotp]

Dear Experts,

Today I have been joining the central heating plumbing in one half of my flat to that in the other half, where my new boiler is.

This was an awkward spot to work in. I was pleased to finish without setting fire to anything. Well, that’s my excuse for messing up and having a leak from one of the solder ring joints.

The interesting thing, and reason for posting, is that the joint seemed fine when I initially filled the system with cold water, at up to about 1 - 1.5bar. It failed when I turned the heating on and it first experienced some hot water. My guess is that part of the joint was sealed with flux or some other crud that was dissolved by the hot water.

My concern is this: I have a lot of new pipework that I pressure tested to 4 bar as I was going along before building the floor over it, but only with cold water. Now that this is finally connected up to the boiler, might I have other leaks in now-hard-to-inspect locations? Or should a 4 bar pressure test have revealed all potential leaks?

Thanks.

 

[Wayners]

I think it expanded with heat. Not a good seal with solder and it split.
The biggest mistake people make when starting out is panicking, pinning the torch directly onto the fitting, and cooking the flux into a black, charred crisp. Once the flux burns off, the copper oxidizes immediately, and the solder simply will not take as it just balls up and rolls onto the floor, so they keep dumping more heat and more wire at it.

Letting the pipe do the work pulling the flame back and testing the joint with the wire means you're using the copper's retained heat to melt the solder. If the joint is hot enough, capillary action pulls the solder right into the socket like a sponge.

I try not to have heat and solder at the same time. Sometimes you have to.
Sometimes you don't like how it looks and need a bit more solder and heat but don't overheat it.
It's comes with practice and confidence.
This guy is quick and on it. You won't be this quick but you get the Idea..

 

[endecotp]

These are solder ring fittings.

 

[denso13]

Or should a 4 bar pressure test have revealed all potential leaks?

It should have and there isn't a lot more you can do to test them. Although I've seen a few with only flux, forgotten to solder I suppose, that last for months before leaking.