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One hydronic zone out of five gurgles

vtfarmer Member Posts: 100
Fascinating forum and great people/information here, thank you all for making this resource available. I wish I'd found it sooner.

I have a small zone (3 Myson panel radiators) for half of one side of the upstairs of my house which I cannot get the radiators to stop gurgling. Every time the zone kicks on it gurgles. If I bleed these radiators until no more air comes out it's usually fine until the zone stops calling for heat then when it starts again it's back to square one (more gurgling and more air will come out). The zone on the other side of the upstairs has older cast iron radiators which have no air come out when I open their bleeders. The other five zones, one of which has three more Myson panel radiators, don't gurgle and don't have any air come out if I open their bleeders.

What should I look for and what would you all suggest I try to stop this? I've bled and bled and bled - probably 20 zone on/off/bleed cycles and gotten it to more or less stop, but I had a circulator fail and also needed to modify another zone to split it into two (did this by adding zone valves) and introduced some air when I did this and now I'm trying to get all of the air out again and am wondering why this zone in particular has this problem.

Here are some more details: this is a fairly complex setup for a residential system. There is an oil fired cast iron boiler which is rarely used and an outdoor wood boiler connected through a plate exchanger to a primary/secondary loop setup. All of the zones come off of this big loop as do the two boilers (one direct, one to the HX). There is a cast iron air scoop on the loop running through the oil boiler but since that loop is rarely activated it doesn't see any flow most of the time. I've manually run the circulator for the oil boiler loop while some of the other zones (including the problem one) were on to try and catch any entrained air bubbles but very little air came out when I've done this. When I did the work referenced above I forced the oil boiler circulator on for a while and the scoop did expel a fair amount of air but the gurgling in the problem zone persisted after the scoop wasn't catching anything else. I also bled all of the other radiators after this work and other than the zone I drained to split into two, none had any air.

I've considered adding another air scoop or one of those microbubble separators up high in the problem zone, but that seems unneeded as the other elevated zone doens't have this problem nor do the other zones including the other one with Mysons. From experience, if I keep bleeding the small Myson zone it will stop gurgling again, but probably after about 20 bleed cycles and I'd like to avoid having to do that if at all possible.

Thanks for any insights in advance!


  • Zman
    Zman Member Posts: 7,495
    What is your system pressure?
    Are you pumping towards the expansion tank?
    A picture of the boiler room piping would help.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • kcopp
    kcopp Member Posts: 4,305
    If you can... inject a 1/4 cup of dawn dw detergent into the system.
  • hot_rod
    hot_rod Member Posts: 20,790
    Properly installed in the correct location it's tough to beat a micro bubble type air purger. If the fluid passes thru it it will grab micro bubbles that are smaller the the eye can see.

    Boosting fill pressure can sometimes help get that problematic air.

    If you have an 1/8 opening the Hygrocals work great, they are both a manual and auto vent.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • vtfarmer
    vtfarmer Member Posts: 100
    I'll get some pictures in the morning, in the mean time here is an old picture of the primary loop with only the oil boiler and one zone connected:

    The air scoop is on the outlet of the oil boiler (behind me in the picture), the circulator is on the inlet to that boiler. The expansion tank is connected to the bottom of the air scoop.

    The system pressure is just shy of 20psi, which is a little high given the house is only two stories plus basement but I left it there to try and help get more of the air out.

    Talking through it to post here is helpful, I think I see my problem: since we added the wood boiler, there is normally no flow through the air scoop and therefore no way for the air to auto-purge! As for why only the upstairs Mysons gurgle and consistently have air to bleed, they're the smallest diameter path highest in the system (the other Mysons are downstairs and at basement level) so maybe the higher velocity in that zone is pulling the air bubbles up there more than they would get pulled anywhere else? If I cut a microbubble separator into this zone then maybe it will solve my problem and serve the rest of the system as the zone runs often (more than the existing scoop is, anyway).

    That little auto/manual vent looks neat, I may put some of those on my radiators with 1/8 tappings - thanks!
  • Zman
    Zman Member Posts: 7,495
    I'm not nuts about the piping. as the water moves around the loop, there is a drop in temp to each zone.
    If it is working and you want to keep it, I think you need to add an air sep on the main loop. Where it is placed now, it will only remove air when the boiler is running.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • vtfarmer
    vtfarmer Member Posts: 100
    My lesson learned is had I known I would be effectively abandoning the oil boiler for wood heat I would have put an air eliminator in the primary loop. Modifying that thing would be a cast iron pain in the tail so I'll put one in the problem zone as described above.

    The piping may be counter-intuitive but works extremely well: the zones flow so much less than the primary loop (3/4 or 1 inch versus 1.5" in the primary) that even with all of them running the one farthest from whichever boiler is supplying heat still gets fluid no more than 5-10 degrees less than the first. The piping assembly heats this part of the basement since it's always hot, which allowed me to not have a unit heater there (and the floor directly above is nice and toasty). In the summer the DHW comes from a heat pump, so it's only radiating heat October-April.

    Further on the loss side we heat with wood which we cut on our farm, so the heat source is "free" if you discount a little time on the tractors and with a big splitter. I get the sense that most of the people on here live in the suburbs or where this isn't practical, but if you have the land/wood and with today's gassification wood boilers it is an awesome option.