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Help needed - constant air in hydronic loop in 1950s house.
Hi all, thanks for your time.
About a year ago I bought a fixer-upper 1950s house in the northeast.
I have cast iron rads in the 1st and 2nd floors, and copper with fin baseboard in the basement.
1st and 2nd floors are on one loop, basement is on another. I've only ever turned the basement loop on twice, to test.
When I was fixing up the house, I had a plumber replace the original 1950s boiler with a new one.
Ever since moving in, I have not been able to eradicate the noise of gurgling and bubbling in the pipes.
It gets way worse as it gets colder and the boiler works harder.
I have bled every radiator many many times, I only ever get a clear stream of water. Even after bleeding multiple gallons at a time, the air persists.
I have also purged the loop with the purge outlet the plumber installed.
One thing I noticed is that the system seems to be running in reverse, have old style monoflo tees under the rads in the basement, and according to the marking on those tees, the water direction is wrong. I'm not sure wether this is an issue or not, the system has no problem heating the house, it can just get very loud with all the gurgling.
My circ pump is on the return under both of the zone valves, and above the pump and below the zone valves is an automatic air vent. The cap is screwed on loosely. I suspect the placement of this air vent may be allowing it to suck in air when the pump runs hard, but I cant confirm this. I have closed the cap on that and let the boiler sit with the pump and heat off to see if I could get the air to rise to the top floor but still see a clear stream of water. The only thing that could be a clue is that the water seems "fizzy" when bleeding at the top floor bathroom rad, it seems this rad receives the most pressure.
I'm wary to keep bleeding and purging, as I know the older the water the better, and new water could start corroding the old cast iron rads, and introduce its own microbubbles.
Any help would be appreciated - this noise is driving me absolutely crazy (Im sure some of you can relate)