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Help! My boiler leaks

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I'm about at wit's end trying to patch the leaks in my boiler and need suggestions. It's a 3/4" scale climax as designed by Kozo Hiraoka. I've been plugging leaks for about a dozen heating rounds now, and I've got one leak that keep recurring, and one that's just really hard to get to. The leaks are very small, the boiler will hold 100PSI for several minutes. I'm using a big sievert propane torch, with a 32mm tip.

The recurring leak is on the foundation ring. That's the first picture. The solder looks good, but the water springs from the center of an apparently solid flood of solder. When I patch this, I've been using a dremel to grind down to bare copper, then melting a 1/4" piece of solder where the leak is. Three times, same result. I don't understand. On this leak, I don't know what to do other that keep trying. Any suggestions?

The hard to get to leak is inside the firebox, around one of the flue pipes, way in the deepest corner. It's shown in the second image. I can't melt solder back there. The flame doesn't want to go way inside, and the whole inner box heats up.  The solder just won't melt in the back, but I'm afraid joints will melt in the front. With this leak, I think I'm going to heat the whole inner box up as much as I dare and then use a spot torch with mapp and oxygen to melt a ring of solder.

Does anyone have any other suggestions? I've come too far to fail. I'm very worried.

My wife suggested radiator stop-leak, and after I told her that I couldn't do that, I started wondering why I couldn't? Why not?

The third image is a shot of my dog checking out my progress to date.

Back when I did my New Shay, that foundation ring was the one I struggled with the most. Grinding it out to the bare metal was the right thing to do, gives the best chance to fix it. One possibility - you mention it was a big area of solder, is there a large gap that you are filling with the solder? If so, a better way would be to grind it out again, and make a small copper piece that fills the gap closely. The silver solder is not good at filling voids, anything more that a tiny crack needs to be filled with metal first. I have had a number of places like that with a seemingly narrow gap that the solder would not fill properly, only solution was to hammer some copper wire flat and push it in, then solder it again.

Which silver solder and which flux are you using? I find that for repair spots like that it works better if I use the 'Easy' or 'Extra Easy' grade of silver solder, since it melts at a slightly lower temperature but more importantly it seems to melt to a lower viscosity and flows into gaps better. For flux, there are a lot of choices, I've settled on the Harris Black flux, before that I was using the Tenacity 5 white flux, before that the Harris White. Each step up gave longer heating time before the flux burns off and stops working.
Hope some of that helps. The model overall is looking great!

I'm using Harris Safety Silv 56. I am also using the black flux. And yes, under all that solder is a relatively large hole, maybe 15 thousandths wide. I was hoping that once I'd filled it with solder it would quit being a problem. If I can find it, I could drill it out and insert some wire.

Yeah, thats pretty wide to fill with just solder. Better to fill it with some copper first - either hammer some wire flat, or trim a slice off a larger bit of scrap and file it to fit. Thick chunks of the solder tend to hold gas bubbles and such, you want to have gaps down to just a couple thou.

As for the other leak up inside the firebox, I had similar issues with staybolts up there, finally got lucky. I don't have any tips for that one.


--- Quote from: crueby on November 10, 2023, 07:16:09 PM ---As for the other leak up inside the firebox, I had similar issues with staybolts up there, finally got lucky. I don't have any tips for that one.

--- End quote ---

Make yourself a boiler tube expander and expand the tube a little against the inner tube plate.



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