Leak in Copper Pipe-why won't solder stick?

Old 06-16-08, 11:03 AM
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Leak in Copper Pipe-why won't solder stick?


Last weekend I installed a new hose bib with less than perfect results.

I sucessfully soldered on a copper adaptor for the bib and had one leak-free joint on one side of the shut-off valve.

I turned the water back on and noticed a leak on the other end of the valve.

I turned the water back off but still had water leaking due to the residual water in the pipes. I cleaned the joint, put on a new coat of flux, and tried to re-solder the joint. None of the solder would stick to save my life.

Will somebody please give me a technical reason as to why the new solder wouldn't adhere? Someone told me that the water was keeping the joint from excepting new solder.

Old 06-16-08, 11:21 AM
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If the solder won't stick, it is either not enough heat, pipe and fittings not clean or fluxed properly, or water still in the pipe.

If it is water and you can get it out, do so. If you can't get it out try to boil it out. If it is a constant drip that will not stop, the big box stores sell an item to aid in this. But I have a solution that is just as good, much quicker, no need to go to the hardware store, and you will most likely have this in your kitchen. Make sure to have everything ready before attempting this trick of the trade. Take some Bread and ball it up, then stuff it into the pipe. You must work quickly here, make sure the pipe is still fluxed OK, then put fitting together and solder immediately. After soldering is complete and you turn the water back on the bread will disintegrate and be forced out with the water pressure.

The only other thing that could happen is if the place you are soldering is closed so as you solder you build up pressure forcing the solder to blow out of the joint. Open the valve downstream so it can release the pressure while soldering.
Old 06-16-08, 11:24 AM
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If there's still any water in the pipe in the area of the solder joint, it will not allow the pipe/valve to get hot enough to solder. Maybe a pro could do it with a hot enuf torch, but the rest of us need to get all the water out of the pipe/valve.

Cut the water off, take the bonnet off the valve and dry it out. Open the valves and use a shop vac to suck air thru til its dry or get in there with a rag to dry it out real well.

EDIT: What Mark said, he knows better than I.
Old 06-17-08, 07:59 PM
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I'd say with 99% certainty that your problem is water in the pipe. Even a little water will suck the heat away from your joint and make it seem like it will never heat up enough to melt the solder.

You may have to cut a piece of pipe out and start from scratch if you can't get the water out of the pipe and keep it out while you solder.

In some cases, you can use MAPP gas (yellow tank instead of the blue propane). It gets much hotter and can boil out the water, as long as it's not refilling from somewhere else.

Good luck! It'll be frustrating for a while... if it gets too frustrating, cut the whole joint out and start from scratch.
Old 06-17-08, 09:24 PM
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Like Zorfdt said, use Mapp Gas, I had the same problem when soldering my mixing valve.

I used a Mapp Gas Cylinder and it boiled off the water and got everything hot enough to get a good solder

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