question about Honeywell SuperVent 1-1/4 air eliminator

ThisSemiOldHouse

I have a Weil-McLain gas-powered Gold CGi water boiler and a Honeywell SuperVent 1-1/4 air eliminator is mounted to the top of the boiler's expansion tank. A few minutes ago, at the very end of a heating cycle, the no-clog vent portion of the SuperVent (indicated in accompanying photo by the yellow arrow) was making bubbling noises, and in glancing at it while the noises were happening, I noticed that some actual visible bubbles could be seen sort of oozing out of the right end of the vent, right by its small threaded cap. Is this normal? I wasn't sure what to make of it, but I shut off the heating system at the thermostat just in case. When the bubbling (which could both be heard and seen) was occurring, a heating cycle had just ended. At that moment, the boiler pressure was around 23 psi (up from around 17 psi when the heating cycle began, as it is a three-floor house), and the temperature had topped out at approximately 190 or 195 degrees Fahrenheit... although I've likewise noticed that after the boiler cuts off at the end of a heating cycle, the temperature on the gauge continues to climb a bit (maybe another five or seven degrees), before it begins to drop continuously.

Anyway, is the visible bubbling at the tip of vent something to be concerned about? And is there any action I need to take to correct it? I don't recall that happening before, although I did hear bubbling sounds a few times earlier, and it could be that I just didn't see any actual bubbles that time. The bubbles weren't so plentiful that anything actually dripped down onto the top of the boiler — but then again, I shut the heat off right afterwards, so I don't know how long it would have continued. Anyway, before I turn the heating system back on, I just wanted to make sure that the issue in question is nothing that could potentially become dangerous. Thanks.
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HomerJSmith

A few photos further back of your sys would help. The cap should be loose and air coming out is normal for a time. Not continuously. 17 psi cold to 23 psi hot is a big jump. I think your temperature is too high. 180 deg would be better. Any jumping of the needle on the pressure side of the gauge when the temp get to about 195?

ThisSemiOldHouse

The bubbles oozing out from the cap only lasted for a few seconds, but I shut the heat off as soon as I saw that. Since it never happened before, I'm guessing it was because of the high temperature for those couple of minutes. I've since lowered the cold psi to 15. Do you think turning the heat back on now to check how things work will exacerbate the bubbling? I'm hoping that the maximum hot temperature reached now will be a little lower (around 180, as you said) as the result of the slightly reduced pressure.

HomerJSmith

Do you have a motorized vent damper on the flue pipe. I assume that it is a cast iron boiler. For a 3 flr house keep the sys pressure to 17 psi cold. Air coming out or spitting is normal until the air is eliminated from the sys.

The bladder tank air charge pressure should match the sys fill pressure.

Lowering the sys pressure has nothing to do with the boiler running at 190 deg. Lowering that running temp would be done by an adjustment in the aquastat.

hot_rod

As long as the spitting stops at some point. The vent discharge should not continue to dribble.

If so it usually is dirt or piping debris in the small needle type valve under the hood.

Entrained air will be driven out of solution as temperature increases. At some point a purger like that should provide a 100% air free systems. Assuming no air is entering?

ThisSemiOldHouse

Thanks for the info. I should clarify on the 195-degree temperature reading I was getting. The boiler actually typically cuts off at around 177 degrees, give or take a couple of degrees. What I mean is, that's where the temperature is usually at during the exact moment that the boiler switches off during a heating cycle. But, for whatever reason, in the one minute (or maybe 90 seconds) following the boiler actually shutting off, the temperature usually continues to rise fairly rapidly for approximately another 17 degrees or so. (Again, this is during the first minute or so *after* the boiler switches off.) Then, immediately after that short interval of rise, the temperature consistently and steadily will typically decrease back to about 110 degrees. As all of this is happening, there is no similar rise or movement in the pressure reading. Instead, the pressure reading slowly decreases as soon as the boiler switches off.

The bubbling hasn't happened again, thankfully. I think it was just that one time because in that particular instance, the temperature was getting very close to 200 degrees, and that was while the boiler was actually running.

HomerJSmith

The reason that I asked about a vent damper is because that can trap hot gasses in the heat exchanger, releasing more stored heat into the water after burner shutdown.

If you have a lot of carbonate build up on the water side of the HX, the cast iron can't release heat energy into the water as fast as it should. That heat energy gradually works it's way into the water raising the temperature (overshoot). Do you have hard water?