Leaking sections on steam boiler with copper header

While copper is not ideal, if there is only one riser out of the boiler, it can't pull the sections apart. In any case,I would have expected the solder joints on the copper to give before the boiler sections. You need to have someone inspect the boiler block and determine if the leaks are actually from the seals or if there is some cracking in the cast iron sections. Have you used and additives in the boiler that could have affected the rubber/composite seals that WM uses between its boiler sections?

Actually, I can envision at least one piping arrangement where a copper header with only one riser could lead to pulling the boiler apart: where that one riser is at the opposite end of the boiler from the equalizer. That, without swing joints, could do the job.

You cannot create a swing joint in soldered copper, as there is no "give" torsionally in a soldered joint, and the pipe itself is very rigid in torsion. You can create an expansion loop, but the legs of the loop have to be long in relation to the diameter of the pipe to keep the reaction forces within reason. You could use an arrangement of at least two flanges, but both would have to be loose enough to allow twisting -- which would almost inevitable lead to leakage after time. Better to do it right the first time, in threaded black iron.

Now, all that said, the leakage which you are seeing may well be between sections. It could be from expansion forces pulling the sections apart, although the tie bolts should be managing that. It could also be, sorry to say, that when the sections were assembled the O-ring (which has a square cross section) which is supposed to seal them got twisted. Wouldn't be the first time. It could also be that the tie bolts for one or more of the sections have lost their preload (the fact that it leaks on startup sort of suggests that).

The bad news is that once leakage begins between sections, there may be enough damage from the leak that the both sections are scrap...

After 8.5 years of service, it's hard to believe that the seals were twisted or there was a defect during assembly unless the boiler "seeped" all along and it was just never noticed. Something seems amiss with this boiler. I know @Jamie Hall suggests that it is possible that the sections could separate with the boiler riser on one side and the equalizer on the other but even that seems a stretch given one attaches to the top of the boiler and the other attaches to the bottom but I suppose anything is possible.

@johnmusgrave

Hard to tell whats going on maybe you can post some pictures.

Remove some of the boiler jacket, if the gaskets are leaking it's probably worth fixing, if there is a hole in the boiler it's not