repeatedly getting air into baseboard hot water - need to find root cause

frumpf · 5:33PM

Hello - I have 3 zone NG boiler hot water heating. 1 zone (first floor) keeps getting air and the pump stops working. Have had multiple HVAC services, pump replace 2x, and they all bleed the system and then it works for about 2 months and then quits again. None of them seem to know how to diagnose to find and fix the root cause. Other 2 zones work fine; have never failed. System also has a "4th zone" superstore hot water tank. Appreciate any advise on how what might be the root cause, how to diagnose, and resolve. Picture of system attached. Thank you!

DCContrarian · 6:47PM

Water is leaking out somewhere in the system.

DCContrarian · 6:50PM

Sometimes you can find a leak by pressurizing a system with air, not very much, maybe to 30 PSI or so. Air makes a hissing noise when it leaks unlike water.

hot_rod · 6:57PM

it could be the fill valve is not maintaining pressure as air bleeds out. What pressure in on the boiler?

Or the Sprio is stuck or plugged and not finishing the microbubble removal

mattmia2 · 7:07PM

i was hoping someone would have better answers, but the first thing to do is to shut off the water feed and see if it maintains pressure. a leak and fresh water with dissolved air is one way it can get more air but issues with where the automatic vent(s) are installed is another.

do you bleed the air out to get it circulating again or are you purging with a large amount of fresh water?

if you bleed a couple times and it still keeps coming back after you burp just the air bubble out then it is getting air in somehow. it is possible as @hot_rod alluded o that the auto air vent isn't working and the air that is in the system instead of getting removed collects in one spot until it can't circulate and you aren't actually getting more air but are just not removing the air that cam with air from purging or filling the system.

it isn't a circulator, that isn't a way it can become air bound.

Jamie Hall · 7:41PM

At the risk of adding an obvious comment — the air can't get in once it's out unless somewhere in the system the pressure is less than atmospheric… the only other possible source would be the expansion tank bladder leaking into the system…

mattmia2 · 8:50PM

https://forum.heatinghelp.com/discussion/comment/1893119#Comment_1893119

or makeup water.

repeatedly getting air into baseboard hot water - need to find root cause

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