Steam rad freaking me out.

Nick W

When this steam boiler first fires, after it's been down awhile, I get steam to the first few sections of a rad on the first floor. Then the vent starts sucking in and the rad cools. The boiler still runs and steam travels up throughout the rest of the system. I can see all of the short piping run to this rad and have even removed it from the wide-open valve and still not had steam show up.

Two risers on either side of the tee feeding this rad get red hot and this branch goes cold.

If I shut off the boiler and let things cool for a while, I get tons of steam out of the valve, until it stops venting and starts sucking in again.

Any ideas?

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Steamhead

There's probably an obstruction in the runout or riser

that's causing a puddle of water to gather until it's big enough to condense the steam as it comes thru. The vacuum you're getting is the steam condensing. Flush out the runout and see if that helps.

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Nick W

Thanks, steamhead.

But that's not it. I'm pretty sure it's a simple case of demonic possession.
Going back today. I think the boiler may be too small.

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Nick W

For what it's worth...

I did a system demand calculation today and the boiler came up over 40,000 btu short.
The plot thickens.

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Christian Egli

Its an optional radiator! There.

Could it be the vent? Has this been a long standing problem?

This is a one pipe system? right? Is the branch piping big enough and sloped the right way to carry both the steam and the condensate at the same time? How is the tee connected to the main, does it get flooded by condensate in the main? Is it in a turn? If there is a wet return, could the water A level rise enough to cause a blockage?

If it is a boiler size problem, can you close off enough radiators to cut 40000 BTU/h and see what happens? Is 40000 even significant compared to the size of the building?

It seems like the problem is related to the speed at which steam is flying past the tee. The faster it goes, maybe the more difficult it is for the steam and condensate to criss-cross into the tee.

What if, by some fluke of design or perhaps rust build up the large main and small tee-off turn into a setup like an air brush. The blowing steam causes a suction into the branch. No steam for the radiator. Do you think the steam flows too fast? You could slow it down by cranking up the boiler pressure! Gaaaa! I did not say this.

Could you feed the radiator from one of those two risers? Maybe a larger tee-off, more streamlined? Maybe a separate drip for the condensate returning from the radiator, a mini wet return connecting to the bottom of the main?

I hope you'll find at least one useful idea in my jumble.

By the way, it is very hard to exorcize a boiler. The wooden stakes just don't do much good at piercing their cast iron core. Try placing a mirror in front of your radiator to see if you can get a reflection, at least that's always foolproof.

Let us know more. Good luck.

Christian Egli