December 22, 2016

Is there a way to manually release air in an automatic air vent?

Yes, there is a way, and we recommend against it!  Read on. All of the Caleffi 5020/5021 Series MINICAL, 5022/5023 Series VALCAL and 551 Series DISCALAIR automatic vents have a spring-closed air release valve under the air vent cap. Most of our air separators and air/dirt separators, such as the 551 Series DISCAL and 546 Series DISCALDIRT have the same mechanism.

BEFORE YOU TRY WHAT IS DESCRIBED BELOW, KNOW THIS: We do not recommend manually letting all the air out of a vent; maintaining the air pocket under the vent cap is important. If the air pocket is eliminated, water and any debris that is floating on top of the water will get into the small vent valve/opening and could cause malfunction (sticking open or closed) and then you'll have to disassemble and clean the vent.

When you unscrew the air vent cap you will see inside a small, white plastic stem holder. The mechanism works like the air valve on a bicycle tire. Using a pen or small screwdriver, if you push down on the stem holder to un-seat the spring-closed valve, you'll vent the air pocket. Again, see above!

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Blog post comments
January 03, 2018

This is a novice question. If I want to release do I do it when the boiler is running or do I turn it off?

Cody Mack

In reply to by Keith

August 09, 2018


Either way will work.

If you're going to do this with the boiler running just be careful as the water could be very hot.

Cody Mack
Applications Engineer
Caleffi North America

February 08, 2018

Should I manually release some air after the initial installation and then snug cap back on?
Thanks for your advice!

Cody Mack

In reply to by Rich

August 09, 2018


After initial installation the valve should be releasing air automatically but you can double check with the manual procedure as well. If the cap on the air vent is tightened down it will not be able to release air automatically. Typically the cap is left slightly loose.

Cody Mack
Applications Engineer
Caleffi North America

Eugene Barufkin
November 15, 2018

Which low cost, under $11.00, bleed valves can be installed horizontally?

Gary Godish
February 12, 2019

where can I buy a Minical 5021 auto air vent with 1/8 in check valve. I live in ZIP Code 15946.


In reply to by Gary Godish

February 14, 2019

Gary, you can contact our Rep in Cleveland, Campbell Equipment Company, at 866-779-5151, to ask about your best source for the 5021.

February 03, 2020

I have the Caleffi 5020/5021 Series vent on my indirect fired water heater. There is a slight leak, a little dribble of water every few mins. Should it be replaced, or can I let it go for a bit? I don't know how necessary the vent is to the system. Thanks.


In reply to by Matt

February 12, 2020

Hello Matt, You can replace the air vent and that may be your best option, however that model is servicable. You could try removing the top and float assembly, clean any debris from the body and float mechanism and reinstall to see if that would correct he issue.

December 04, 2020

I get a lot of gurgling sounds from my heating system which leads me to believe that I have a fair amount of air in the system. I have a 5026 or 5027 attached directly above the expansion tank, next to my boiler (in the basement). Is it better to have the air vent where it is or should the air vent be located at the highest point in the system?


In reply to by Terry

December 30, 2020

Terry, that noise could be consistent with excess air in your system. Adding an auto air vent at a high point where air is collecting could help. Also you may want to consider our 551 Discal air separator. This product has a coalescing mesh element that will separate the air from the water and remove it. It is a multi-pass device and is more efficient in removing air. The air vent typically does not separate the air from the water it simply removes air that migrates into the vent body.

Paul Jones
February 09, 2021

My boiler is losing pressure every day, main combi boiler, no noticeable leaks, I’ve topped up expansion vessel, but when on its up to 3 bar and dripping like mad outside, do you think it’s a prv issue or expansion vessel fault? The error says to top up and check auto air vent.

Getting new boiler in couple of months and I’ve read as a temporary fix I could maybe drain a radiator to put air in it and get pressure that way?




In reply to by Paul Jones

February 11, 2021

Paul, One way to test this would be to shut off the auto fill to the boiler and see if pressure increases in the system. If the pressure increases with the autofill shut off then it is more likely thermal expansion and not a PRV issue. If the pressure stays stable then that may indicate you have debris in the PRV causing it to over pressurize.

Bob Ilines
February 07, 2022

Will an auto air vent allow air in if fitted at a high point on the return of a boiler bypass loop?



In reply to by Bob Ilines

February 07, 2022

Bob, An auto air vent can be placed on the supply or return side of the system and typically installed at a high point in the system. As long as there is positive system pressure it will not allow air back in. If it is at a point where there is a negative system pressure then it could draw air back in through the vent. Caleffi does offer an "Anti-Suction" cap for air vents that end up in that location under part number 562100.

January 12, 2023

Our auto air bleeder was leaking water so we installed a new one… a day later there is a small pool of water on top of the new bleeder… could it be condensation? Or is this bleeder faulty as well?

March 21, 2023

RJ, the reason that water would be coming out of an air vent is usually if there is a little piece of debris caught in the seat. This can usually be fixed by removing the cover with the float and linkage, and blowing compressed air from the outside in through the "bleeder". If a little piece of rust or a copper shaving or something is caught in there, it will leak water.