How to Replace Leaky Automatic Air Vent


Old 11-28-04, 07:04 PM
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Join Date: Nov 2004
Location: NE Massachusetts
Posts: 234
How to Replace Leaky Automatic Air Vent

I have an oil-fired hot water baseboard heating system. It has an air purger with an expansion tank screwed into the bottom and an automatic air vent on top of the air purger. The air vent is leaking some water. Based on tapping the expansion tank it does not seem waterlogged (bottom 2/3rd of tank sounds hollow or empty). So I think just the air vent is leaking. How do I go about changing it? I don't see any valves that allow me to isolate the air purger from the rest of the system. I assume the air vent is at system pressure (12 - 15 pounds) and that I will need to depressurize or partially drain the system so I don't get an unwanted, very hot shower. How much water do I need to drain from the system? Can I just use the automatic water make-up device to refill the boiler? I assume I will need to bleed the baseboard radiators afterwards. The air vent looks rusty where it attaches to the air purger body. Do these things tend to really stick and be difficult to remove?
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Old 11-29-04, 05:35 AM
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Join Date: Dec 2002
Location: Easton, PA
Posts: 3,245
I would suggest that you turn off the boiler for an hour to let the water cool off a little. Then turn off the water to the autoimatic feeder and put a bucket under the relief vave and trip it. You should only get a couple of quarts of water out until the pressure gauge shows 0. The water will slow down at that point. Get the new vent ready with a little thread sealer. If you use teflon tape, keep it back from the end of the threads. Crack the old vent loose. It is only a 1/8" pipe thread so it won't be that hard to get loose. Trip the relief valve one more time and go for it. Once you put the new one in the hole, you will only have a trickle of water until you get it started. Snug it up and you will be good to go. Open the automatic feed and turn the boiler back on. You should not have to bleed the radiators. You only really took out what was in the expansion tank.

Old 05-01-12, 05:14 PM
Join Date: Oct 2010
Location: USA
Posts: 121
This just happend to me..The air vent atop of my expantion tank wont stop dripping water! I noticed when i run the heat today it sounded like running water going through the pipes..So i take it the boiler is low due to the leaking air vent? Following these instuctions will work for me to replace the vent?

Thank's for your help...
Old 05-01-12, 06:11 PM
Join Date: Dec 2010
Location: USA
Posts: 172
Others will chime in , but the questions will be what kind of air vent is it and post some pic's of the boiler and pipes with a few wide ones to get it all in. Some like a spiro vent can be cleaned. Mine was leaking and I capped the end so it would not drip. Bought a new one and took the cap off and was going to change it and it had stopped leaking. I have done 2 repairs on the boiler and it has purged the air and not leaked since. Now I have a spare.
Old 05-01-12, 06:51 PM
Join Date: Oct 2010
Location: USA
Posts: 121
Some pics..The one thats leaking is the one on top of the expantion tank. It only leaks when the boiler is running and calling for heat. The expantion tank has been replaced sence these pic's
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Larger pics can be found in this thread
Old 05-02-12, 04:26 AM
Join Date: Oct 2010
Location: USA
Posts: 121
Looks like i need one of these right?

1/8 in. Hy-Vent-400-3 at The Home Depot
Old 05-03-12, 04:05 AM
Join Date: Oct 2010
Location: USA
Posts: 121
All done


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