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My system looks exactly like this. I believe it's called Hydro Air Heat. See that thing with the green rectangle around it. It started spraying hot water from that nipple on top (indicated by the green arrow).

First of all what is that thing called and what is it's function? Does anyone know that make and model (in case I need to replace it)?

I turned off the heat, closed an intake valve and it eventually stopped spraying hot water. Then I tightened that nipple all the way down and turned everything back on. It's no longer leaking and I believe I have heat. However I don't know if that thing is supposed to be tightened all the way like I have it. Have I locked air in in some way I shouldn't have? Have I ruined some kind of pressure controlling apparatus? Or was I supposed to tighten that nipple all the way for normal operation?


It's a Bell & Gossett Air Separator. If you run your system with the nipple closed then it does not do its job and air bubbles are trapped making your system less efficient and shorter lifespan. But tightening down the nipple does not render the system unusable or in danger of immediate break-down.

It's a Bell & Gossett Model 11211x. The reason for the 'x' at the end it that it seems like it has been discontinued from the Bell & Gossett website here. At the site you see a picture of it in a group of other items, but if you click the picture you see the other items but not this one.

One suppler seems to still have some in stock here. And maybe this one as well. They seem to think it is SKU 112113 or 112112, but others seem to have a slightly different picture of the 112113 SKU.

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