Replacing hydronic system air vent valves

arctic_colors

Hi everyone — my heating system seems to have two air valves near the boiler, a tiny one sticking out from the boiler itself and a Taco 4900 attached to the expansion tank. I think both are stuck and need to be replaced, the pipes gurgle like crazy whenever the heat is on so I assume there's a ton of air in the system. I loosened the little screws on the valves and a ton of air hissed out, followed by constantly leaking water until I tightened 'em back up. Our water is pretty hard and I've had to replace almost all the faucet cartridges since moving in, so it wouldn't be surprising.

ChatGPT (who is sometimes right and sometimes psychotic) says I should replace the head of the Taco valve (with this I guess?) and either replace the little valve entirely (this or this I suppose) or just cap that pipe.

Does that make sense to the real experts here? Can I just shut off all the ball valves in sight, drain the pipes from the valve below the circulator, unscrew & replace those parts, then open the ball valves and refill to the same PSI (approx ~12 psi/30 ft)?

Anything else I should consider before it starts getting cold out? Should I try to flush air out of each zone manually as well, or just let the new air vents do their job? (I don't have bleed valves at the baseboard radiators themselves.)

Thank you in advance!

hot_rod

You can split open that 4900 and see if the float is stuck or the needle valve gunked up. If you hear air in the system but never any coming out of the 4900, something is plugged or stuck. Chronic air problems can be expansion tank related.

I don't know if that top head is serviceable, but you could swap out a new top without removing the entire purger.

Unfortunately you are pumping towards the PONPC with the circulator on the return.

As an experiment attach a washer hose to the valve above the circulator. Remove the expansion tank from the purger, connect it to that boiler drain. now you are pumping away, adding pumps pressure differential to the system piping.

Better yet the tank connected at the fill valve, then it is below that yellow ball valve for service.

The expansion tank, contrary to rumors does not need to be at the air purgers location.

Zone valves off and two valves above the circulator should isolate the fill system, to replace or service. Turn the fill valve off of course :)

The air vent on the boiler certainly does some work, but it does not grab microbubbles from the moving flow like the microbubble purger does. Air purgers and air vents are different animals, different uses.