Heat exchanger material?

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Adkroot

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Trying to apply some solder to the pinhole leak in the tubing on my Bosch water heater heat exchanger and it beads and rolls right off. Yes, I cleaned it, buffed with emery cloth and fluxed. It looks like copper, cleaned up and sanded like copper, but no go on the solder. No problem at all getting the solder to adhere beautifully to the jacket and of course to any of my copper fittings other jobs.
What could be going on with this material that looks like it’s copper?
 

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WorthFlorida

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Solder will not work trying to patch a hole. Solder only works between two same materials. Brazing, as used on AC tubing, is needed but it might just burn through the copper if it lost its annealing.

What you can try is get a piece of copper like a 3/4" or 1/2" coupler. Cut a section out or cut a slot on one side, spread out the coupler then form it around the pin hole. Make a patch like fixing a tire tube, however, some couplings can be really hard to bend. Clean everything, flux it and use a clamp to hold the two parts together, then try soldering it.
 

Adkroot

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Solder will not work trying to patch a hole. Solder only works between two same materials. Brazing, as used on AC tubing, is needed but it might just burn through the copper if it lost its annealing.

What you can try is get a piece of copper like a 3/4" or 1/2" coupler. Cut a section out or cut a slot on one side, spread out the coupler then form it around the pin hole. Make a patch like fixing a tire tube, however, some couplings can be really hard to bend. Clean everything, flux it and use a clamp to hold the two parts together, then try soldering it.
I appreciate the input, and i understand that trying patch a pin hole isn't much of a repair (I only need to stop the drip for a couple days until the new heat exchanger arrives) but in my plumbing work I can definitely say that solder will readily adhere to copper whether it's in the fitting or or on the outside of the pipe. This beads right off. Have a look at the picture where I melted some against the jacket to see if it was the same material as the tubing. It's adhered as it should.
 

John Gayewski

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The pictures on this site no longer support enough definition to be able to zoom in and see any detail.

Is it magnetic? 304 stainless will be slightly magnetic with a strong magnet. 316 in my experience will not, but I've never tried it with a really strong magnet. Most heat exchanger manufacturers use 316 (I think). If it's definitely copper and it's beading off then it's too hot.
 
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