Capping Air Vents?

Baeljb

We have our 15-year old Colorado mountain cabin. Boiler supporting 5-zones of radiant, 2-zones of baseboard, and a domestic hot water tank. Just had our fourth zero pressure with glycol mix leaking out of one of two air vents. Also have one spirovent. Worst case was 10-years ago when both air vents and spirovent were leaking mix. Determined that the boiler manufacturer hadn’t cleaned all casting sand out of boiler and vents were jammed. All pressure losses have been linked to air vents. I was thinking of capping them off and periodically bleeding them manually. We are scared if we lose pressure we will damage boiler. Any negatives on capping vent?

Intplm.

Is your spirovent your main vent? If so , capping the other vents should not do any harm as the spirovent will eliminate most if not all of the air.

What type of vents are leaking? Eliminating the leaking vents will most likely correct any air problems as well as the leaks.

Do you have continued air problems in your system? If so, you most likely have a leak (maybe just those pesky vents) somewhere and that leak will need to be fixed.

Over charging your system with glycol can make some parts in your heating system deteriorate prematurely. So if you have to much glycol in the system this could be the reason for the leak.

Best to get a better quality air vent(s) to replace those that are leaking and be sure to properly charge your system with non-toxic glycol.

Baeljb

There are three vents. Two Taco by-vent. One on the scoop above the expansion tank. One on the DHW tank. The spirovent is on the input to the radiant supply manifold pump.

I have never seemed to have air issues. When we thought that we had the casting sand issue, all three vents were spewing glycol. Last I looked, the glycol was about 25%. The totally incompetent plumbing firm had it originally at 80%.

Since we may miss two-three weeks at a time, and it gets down to -30 during winter. I am thinking that I would have most piece of mind completely sealing system and occasionally opening vents.

Thanks

Baeljb

What are better quality vents?

Intplm.

Your main vent, if I'm reading you correctly is a air scoop and not the spirovent. Air scoops are virtually worthless. They are old technology and do little for air elimination.
A "microbubble" air separator like a main spirovent, ( there are other brands ) installed in place of your air scoop will eliminate air in your system and will continue to eliminate air in your system.
Where is the air coming from? Most likely the make up water that is being added due to the leaks. In your case its the other air vents you previously mentioned. Get rid of those and replace them with new ones that don't leak.
A low water cut off is also a good idea to add to your system. A low water cut off will shut the boiler down in case of a leak causing low water in the boiler.

Can you post some pictures here to get a look at things?

Baeljb

Right. The scoop/taco is the main vent. Have the auto fill shutoff because I did not want a flood if we got a leak. Also wanted to be able to see leaks. So I cannot see how air would be introduced into system. Installed a TACO LWCO and it’s electronics failed after two years. Planning to replace with McDonnell & Miller. No noise so I don’t suspect air. Figuring if I open vents and spirovent when we are there, we can limit exposure. Not at the home now so I wouldn’t have pics till this weekend. Thanks for your help.

Intplm.

The air is introduced into the system from the cold make up water.
Make up water is cold, and oxygenated. The micro bubbles in the cold water expand when introduced into your heating system and are from the leaking vents that you have described.
The Taco air scoop should be replaced with a microbubble air separator. Taco, Caleffi, Spirovent are a few companies that come to mind that sell these separators. The air scoop is going to continue to be problematic, so get rid of it.
You should also give your system a thorough manual purge and update your antifreeze.

Zman

Capping the air vents as you suggest should not cause any issues.
I like a product like this for second homes with glycol. The system can refill a little if needed without risk of flood or glycol dilution. You can also easily monitor the levels and know how much fluid you are loosing.
https://www.supplyhouse.com/Axiom-MF200-MF200-PRESSURE-PAL-Hydronic-Mini-System-Feeder-6-Gallon