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Expansion Tank / Compression Tank Air Valve Leak Diagnosis & Repair
Water leaks at the heating system expansion tank air valve or air vent
- POST a QUESTION or COMMENT about heating system expansion tanks: their function, size, location, maintenance, and need for draining (on some models)
Heating boiler expansion tank / compression tank air adjustment valve & air vent valve troubleshooting guide:
This article explains the difference between the air pressure adjustment valve on an internal-bladder compression/expansion tank and the a automatic air vent valve found on both bladder type and bladderless type expansion tanks on hot water heating systems. We explain how each of these valves may be leaking but the implications, cause, and repair are quite different.
This article series provides a heating system expansion tank (compression tank) troubleshooting & repair guide.
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Expansion Tank Air Valve vs Vent Leaks
Reader Question: water coming out of the top brass venting/valve atop the boiler's expansion tank
I found information on the expansion tank noted in the subject line on your web page. This is the kind I have on my gas furnace. There is water coming out of the top brass venting thing above the tank. My water pressure cold is almost down to zero.
The unit runs and heats the house but wondering what is going on here something is off. Any suggestions on what to do would be greatly appreciated.
At left we illustrate a new automatic air bleed valve.
[Click to enlarge any image]
Reply: First let's distinguish leaky automatic air bleed valves from a leak at the air pressure adjustment valve on an internal-bladder heating system expansion / compression tank
Water Leaks at an Automatic Air Bleed Valve
The most likely cause of leakage at the automatic air bleeder valve is that the valve core or stem itself has failed or its seat has debris on it, preventing the valve from closing when it should, or the float inside the valve has failed and no longer opens and closes the valve properly.
That leaky automatic air bleed valve should be replaced.
If the part that is leaking on your boiler looks somewhat like the device shown at left, that's an Automatic Air Eliminator - Auto Vent No. 67 from Maid O Mist in our example. (Your heater may use a different brand or product).
If that's the leak source the part replacement is usually a minor repair.
Temporarily you can usually stop the leak at an automatic air vent by screwing closed the valve cap atop the valve. But that will also prevent the valve from venting air and thus can lead to an air-bound heating system and thus to loss of heat in one or more areas of your home.
Therefore while you want to stop any immediate leak to avoid making a mess or dripping onto electrical components, the proper repair is to replace the automatic air vent promptly.
See AIR BLEEDER VALVES for details it's just a hop skip and a jump right over
to AIR BLEED VALVE LEAK REPAIR
Leaks at an air pressure adjustment valve on an internal-bladder compression / expansion tank
However if the leak is not at the automatic air bleed vent (shown in our photo above), but is at the air valve mounted on an internal-bladder type heating boiler expansion tank, then we have a different problem.
Our page top photo shows an internal-bladder type expansion / compression tank used on a hot water heating boiler. In the page top photo a small blue cap on the under-side of the tank covers its air pressure adjustment valve.
[Click to enlarge any image]
At left, that little red cap atop the heating boiler compression tank hides the air pressure adjustment valve. Manufacturers typically ship these tanks pre-charged to 12 psi cold - suitable for most circumstances.
For some heating systems operating at higher pressures the service technician may use this valve to adjust the pre-charge air pressure in this little compression / expansion tank.
What does it mean if water squirts out of the air adjustment valve on an expansion tank?
If the expansion tank you are using is an internal-bladder type and water is coming out of the air charge valve as you describe, I suspect the bladder is burst - it's time for a replacement tank bladder or if that's not an option on your tank, a new expansion tank is needed.
Watch out: before even considering expansion tank replacement, if the water leak you are describing is not at an air charge vent on the expansion tank itself (a part that is indeed not present on most bladder type expansion tanks for heating systems) then you are probably talking not about a problem with the expansion tank but rather a problem with an automatic air bleeder vent - a separate part intended to bleed air from a hot water heating system.
Our photo below illustrates water squirting out of a water tank air pressure adjustment valve. This particular tank is in use on a potable water supply system pressure tank, it is not a heating system expansion tank.
But this is what you might see when pressing the center pin of the air adjustment valve on an internal-bladder-type heating system pressure tank if its bladder has leaked and the tank is waterlogged.
Watch out: unlike the cold water squirting out of a water pressure tank with a burst internal bladder, the water that may squirt out of a heating system's expansion tank will be hot and nasty.
...
Reader Comments, Questions & Answers About The Article Above
Below you will find questions and answers previously posted on this page at its page bottom reader comment box.
Reader Q&A - also see RECOMMENDED ARTICLES & FAQs
On 2020-03-29 - by (mod) - emergency leak repair: tighten the valve cap
Yes definitely, George. If the leak is at the screw cap on the air vent, just tighten the cap down, or if it's corroded and stuck you may be able to carefully
(don't make matters worse by breaking off the valve)
remove it and install a new tire valve stem cap. But do call for repair and get it replaced, as if you lose a working air vent you can ultimately lose heat by having a zone become airbound.
On 2020-03-29 by George
The little air releif valve is leaking above my furnace expansion tank.. Can I tighten it down until I get a plumber
On 2018-09-15 - by (mod) - is the air valve cap kept loose or tight
If the valve is leaking you can make a temporary repair by tightening it until the leaky valve is replaced;
If the valve is used ONLY for adjusting air pressure in the tank it can be left tight.
Watch out: If the valve cap that you're discussing is on an air vent device such as found on hot water heating radiators, convectors, and boilers, then it needs to be kept loose so that the vent can infect release Air from the system.
On 2018-09-12 by J
Should bleeder cap on top of expansion tank be tight or slightly loose
On 2018-09-08 - by (mod) - My air valve on my tank froze
If the pressure tank is a type that uses an internal bladder, yes a regular valve stem that is the right length should work - take the old one to your auto parts supplier.
For other air valves on some water supply systems the valve core uses a softer spring and you wouldn't get a match at the auto supplier. YOu'd match that at a plumbing supplier.
On 2018-09-05 by Isarick Brown
@Jean,
I am speaking of a hot water expansion tank valve stem froze up and I need to check the air pressure but can't?
My air valve on my tank froze on me can't get a reading,can I replace it myself and is it a regular valve stem?
On 2018-03-04 by Jean How can I isolate the Automatic Air Vent.
Radiators needed bleeding.
Pressure in expansion tank was low so opened both valves in loop and added water till pressure 1.5, meanwhile automatic air vent has started leaking and expansion tank pressure is dropping.
When the expansion tank pressure drops to zero will the water stop dripping - or does the water from the Auromatic Air Vent come from somewhere else? (Can't reach the Off tap so continually emptying jugs of water. Please help!
How can I isolate the Automatic Air Vent. It is a Headrae Sadea Amptec Wet Radiator system I have.
On 2017-10-27 - by (mod) -
The valve core is a standard Schrader valve but of course the valve for everybody maybe a shape that is designed specifically to fit the tank.
you might try using a valve core tool to tighten or replace the core inside the valve ste
On 2017-10-26 2 by Leaky Schrader Valve
Hello,
I have a schrader valve on my Extrol Amtrol tank attached to my hydronic heating system whose operating pressure is 12 PSI. The tank is failing to maintain pressure. I have re-pressurized the tank to 12psi and with a bit of saliva was able to see that it is not holding the air in. There is no water coming from the valve just air.
Does the tank utilize a standard size schrader valve so that I can replace it with a simple trip to walmart or something non-standard?
Any tips to replacing the valve besides being gentle?
Thank You
Sam
On 2015-07-29 by Anonymous
Good.
...
Continue reading at EXPANSION TANK LEAK REPAIR FAQs or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.
Or see EXPANSION TANK LEAK REPAIR FAQs - questions & answers postd originally on this page
Or see these
Recommended Articles
- AIR BLEEDER VALVES for details it's just a hop skip and a jump right over
- AIR BLEEDER VALVE FUNCTIONS
- AIR BLEED VALVE LEAK REPAIR
- BOILER LEAKS CORROSION STAINS a catalog of all types of leaks found at heating boilers
- EXPANSION TANKS, BOILERS - home
- EXPANSION TANK AIR VALVE LEAKS
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EXPANSION TANK AIR VALVE LEAKS at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.
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INDEX to RELATED ARTICLES: ARTICLE INDEX to HEATING BOILERS
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Citations & References
In addition to any citations in the article above, a full list is available on request.
- Holohan, Dan, "Why compression tanks waterlog", HeatingHelp.com (June 2014) - retrieved 19 March 2015, original source: https://heatinghelp.com/systems-help-center/why-compression-tanks-waterlog/
- Etherton, Mark (contractor), "Expansion Tanks 101: the facts and myths", Contractor Magazine, contractormag.com, (March 2000), retrieved 19 March 2015, original source: http://contractormag.com/hydronics/cm_column_75
- Extrol Corporation, "Installation & Operation Instructions, Extrol (R) Hydronic Diaphragm Expansion Tanks In-Line & SX-Series", Extrol Corporation, 1400 Division Road, West Warwick RI 02983, Tel: 401-884-6300, Website: www.amtrol.com, retrieved 3/3/2014, original source http://www.amtrol.com/media/documents/extrol/9015183_3_11_EXTROL_IO.pdf
-
Research on permeability of rubber used in internal bladder-type heating system compression tanks or expansion tanks
- Bodell, Bruce R. "Distillation of saline water using silicone rubber membrane." U.S. Patent 3,361,645, issued January 2, 1968.
- Ciesielski, Andrew. An introduction to rubber technology. iSmithers Rapra Publishing, 1999.
- Fuller, James, and David M. Stedham. "Expansion tank with a predictive sensor." U.S. Patent 8,633,825, issued January 21, 2014.
- Martinello, Ermanno, and Mark Weih. "Membrane coating for a water pressurization Bladder." U.S. Patent Application 12/498,128, filed July 6, 2009.
- Stern, S. A., F. J. Onorato, and Charles Libove. "The permeation of gases through hollow silicone rubber fibers: Effect of fiber elasticity on gas permeability." AIChE Journal 23, no. 4 (1977): 567-578.
- Terashita, Fumihiro, Shingo Takagi, Shinzo Kohjiya, and Yasutoshi Naito. "Airtight butyl rubber under high pressures in the storage tank of CAES‐G/T system power plant." Journal of applied polymer science 95, no. 1 (2005): 173-177.
- [4] B&G / ITT Reducing Valves, Instruction Manual V55999: Reducing Valves Installation, Operation, & Service Instructions, Bell & Gossett Air Separators and other heating system components, Bell & Gossett, 8200 N. Austin Ave., Morton Grove IL 60053, USA - Tel 847 966-3700 Fax 847 965-8379. Original source www.bellgossett.com/literature/files/610.pdf
- [5] Bell & Gossett Airtrol® System Installation, Operating and Service Instructions, Bell & Gossett, 8200 N. Austin Ave., Morton Grove IL 60053, USA - Tel 847 966-3700 Fax 847 965-8379. Retrieved 8/9/2012, original source B&G, [copy on file as Airtrol_Installation_Manual.pdf linked in this reference]
- Domestic and Commercial Oil Burners, Charles H. Burkhardt, McGraw Hill Book Company, New York 3rd Ed 1969.
- National Fuel Gas Code (Z223.1) $16.00 and National Fuel Gas Code Handbook (Z223.2) $47.00 American Gas Association (A.G.A.), 1515 Wilson Boulevard, Arlington, VA 22209 also available from National Fire Protection Association, Batterymarch Park, Quincy, MA 02269. Fundamentals of Gas Appliance Venting and Ventilation, 1985, American Gas Association Laboratories, Engineering Services Department. American Gas Association, 1515 Wilson Boulevard, Arlington, VA 22209. Catalog #XHO585. Reprinted 1989.
- The Steam Book, 1984, Training and Education Department, Fluid Handling Division, ITT [probably out of print, possibly available from several home inspection supply companies] Fuel Oil and Oil Heat Magazine, October 1990, offers an update,
- Principles of Steam Heating, $13.25 includes postage. Fuel oil & Oil Heat Magazine, 389 Passaic Ave., Fairfield, NJ 07004.
- The Lost Art of Steam Heating, Dan Holohan, 516-579-3046 FAX
- Principles of Steam Heating, Dan Holohan, technical editor of Fuel Oil and Oil Heat magazine, 389 Passaic Ave., Fairfield, NJ 07004 ($12.+1.25 postage/handling).
- "Residential Steam Heating Systems", Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
- "Residential Hydronic (circulating hot water) Heating Systems", Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
- "Warm Air Heating Systems". Instructional Technologies Institute, Inc., 145 "D" Grassy Plain St., Bethel, CT 06801 800/227-1663 [home inspection training material] 1987
- Heating, Ventilating, and Air Conditioning Volume I, Heating Fundamentals,
- Boilers, Boiler Conversions, James E. Brumbaugh, ISBN 0-672-23389-4 (v. 1) Volume II, Oil, Gas, and Coal Burners, Controls, Ducts, Piping, Valves, James E. Brumbaugh, ISBN 0-672-23390-7 (v. 2) Volume III, Radiant Heating, Water Heaters, Ventilation, Air Conditioning, Heat Pumps, Air Cleaners, James E. Brumbaugh, ISBN 0-672-23383-5 (v. 3) or ISBN 0-672-23380-0 (set) Special Sales Director, Macmillan Publishing Co., 866 Third Ave., New York, NY 10022. Macmillan Publishing Co., NY
- Installation Guide for Residential Hydronic Heating Systems
- Installation Guide #200, The Hydronics Institute, 35 Russo Place, Berkeley Heights, NJ 07922
- The ABC's of Retention Head Oil Burners, National Association of Oil Heat Service Managers, TM 115, National Old Timers' Association of the Energy Industry, PO Box 168, Mineola, NY 11501. (Excellent tips on spotting problems on oil-fired heating equipment. Booklet.)
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- In addition to citations & references found in this article, see the research citations given at the end of the related articles found at our suggested
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