What say you ? She’s steaming

In all likelihood, boiler needs to be replaced. Hard to tell from the video. Are you sure it's coming from the boiler and not from the glass or something like that?

Could be a flange gasket where the pipe covering blows up in size or a union but most likely the boiler. Flood it when it is cold as others have mentioned.

It isn't an emergency but I would try to do it as soon as you can reasonable schedule it. You could probably get through the season on that if you absolutely had to but it isn't the recommended course of action.

Make sure the LWCO and water feeders work.

At this early stage of the heating season, I would recommend replacing ASAP

@New England SteamWorks is excellent.

I don't think that is a part of the hx that connects to the firebox and flue collector, i think it is just leaking out in to the basement.

JB weld or jb weld putty will be fine there because it won't get above steam temps because that part doesn't see combustion products. I wonder if you can mix putty and the paste to form something that won't run but is softer than the putty.

Its time to replace that boiler. To buy yourself some time, use this.

Jb weld? Could work. This stuff will work. Read and follow the directions. This stuff was invented for this reason.

I'm starting season 5 on an old boiler with a leak similar to (though not as bad as) yours. Patched it with JB Weld and a piece of steel formed to cover the hole. Works great and looks the same today as it did 4 years ago. JB Weld handles 200º-ish just fine. Give the epoxy a good substrate to bond to; diligently clean off ALL the rust in and around the hole. Use a vac to suck it up while you work. You don't need the epoxy to fill the hole; encircle the hole with it, embed the steel piece in it, and cover the edges to hold the steel in place. Should get you through the season no problem.

FWIW, here's a pic of my patch.

https://us.v-cdn.net/cdn-cgi/image/quality=80,format=auto,fit=scale-down,height=2000,width=2000/5021738/uploads/editor/z5/8770yibb6af3.jpg

As pointed out above, I misspoke, as this leak is not in the combustion area. So chimney is not of concern in this particular scenario. But steam will absolutely eat away at the inside of chimneys. Of course there is moisture in combustion gases, but the steam will generate considerably more moisture. And will presumably cool down the chimney.