I recently had an issue where my air vent valve hung open and sprayed water all over making a mess. I drained the system and put on a new valve. I then filled the system making sure it was not air bound. At this point there is no air in the system and what ever little air was in the system has now been purged by the air vent valve. The question is this...should I close the cap on the air vent our leave it open? There is an expansion tank on the system. Thanks.

the cap is there ONLY to be closed if the valve starts spitting water and won't stop. in other words, leave it open. put a touch of grease on the male threads so if you need to close the cap you will have a fighting chance.

Air will be introduced into the system when make up water is added. The cap should be left loose.

That's a hi-hat vent. They're fine for removing air from the top of a boiler. They are not a good means of air removal for a system. Get yourself something like a spiro-vent, that will remove micro-bubbles. Scoops are fine, as long as you pay attention to the piping restrictions. There's none with a spiro-vent. Is that hi-hat on top of a scoop?



Edited 1 times.

Yes, vent is on top of air scoop