I've seen a few posts here that mention Burnham IN series boilers that have failed after 10–15 years due to rust perforation above the water line and I think I may have noticed something that might help people get a little more life out of them if I'm right.
First of all, the castings are too thin, but I understand they're trying to improve heat transfer.
Second, I don't have a huge sample size to draw on, and please speak up if you have evidence to the contrary, but they tend to develop these leaks in one of the end sections.
Finally—and this is where I'm on the shakiest ground, but I'm hoping some of you who have replaced these boilers might be able to confirm or disprove my hunch—I think the damage is occurring near the supply tapping. Below is a picture of a failed section that someone posted. I've labeled what I believe is the supply tapping, but the person who posted it wasn't able to confirm this.
So, what I think is happening is that, for some reason, too much condensate is dripping down the supply riser after every heating cycle, and, in combination with the thin casting, it creates a perfect storm for rust perforation to occur.
Condensate is, essentially, distilled water. It doesn't contain any minerals or buffers or additives that might be added to the boiler water. It's just plain water—purer than any tap water that might be used to fill the boiler. Also, if the condensate is just trickling down from the riser, it would form a thin layer as it flows over the surface of the casting, where oxygen is readily available to promote oxidation.
If my hunch is correct, a couple of possible recommendations follow.
- When replacing a boiler that has failed in this manner, installers should be sure to correct any piping that might allow condensate to drip back into the boiler between cycles. There will always be some carryover in the supply risers, even with a drop header. It's unavoidable but also unproblematic, as carryover is just boiler water, not distilled water.
- Burnham should make their end section casting thicker in the area where these failures are occurring. They can keep making the inner sections thin to promote heat transfer, but the end sections are more vulnerable to corrosion because of the availability of oxygen and the possibility of exposure to condensate.
Just another DIYer | King of Prussia, PA
1983(?) Peerless G-561-W-S | 3" drop header, CG400-1090, VXT-24