How to Identify and Correct Air Leaks

WRITTEN BY:  Inyo Pools

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If you are seeing a significant number of bubbles coming out of your return lines into the pool, you probably have an air leak in your filtration system. Possible sources of this problem are low pool water levels, leaks around the strainer lid, leaks in the unions or leaks in the pump seals. For optimum pool pump operation, the source of the leak must be identified and corrected.


Step by Step


Step 1

Your swimming pool filtration system has two sections: the suction side (from the pool to the pump) and the discharge side (from the pump to the pool). Check the strainer pot of your pump. If you see a significant number of air bubbles moving through the strainer pot, you know that the air leak is somewhere on the suction side of the system plumbing before or at the pump.

Step 2

Go over to the pool and check the water level. Ideally the pool water level should be at least halfway up the skimmer intake. If the water level is below this level, the skimmer is probably sucking air into the skimmer pipe to the pump. This is a simple problem to resolve. Simply fill the pool to the halfway point of the skimmer. Also check that nothing is holding up the flap of the skimmer opening to the pool. This could also let air into the skimmer suction pipe.

Step 3

If the pool water level is adequate, your next step is to check the strainer lid on the pump. If it is not on tightly, you may be sucking in air around the lid. To check the lid, first TURN OFF THE POWER TO THE PUMP at the breaker box.

Step 4

Remove the pool pump strainer lid. These are generally screwed on or are secured with toggle bolts. Pull the O-ring out of its groove. Clean out any debris that might be in the groove. Check the O-ring for any cracks or wear. Sometimes an older O-ring is stretched so that it bulges when you try to replace it in its groove. This is a common source of leaks. When you screw on the lid, the O-ring will bulge out and create a leak. Replace a worn or stretched O-ring. Also, it's a good practice to lubricate the O-ring lightly before replacing the lid. Use a good pool seal lubricant (Teflon or silicon). DO NOT use petroleum jelly.

Step 5

If your pool pump strainer lid was not the problem, check the union commonly inserted before the pump. Again make sure that the power to the pool pump is turned off before unscrewing the union.

Step 6

After separating the union, you should see an O-ring in the groove of the union. As mentioned in Step 4, check that this O-ring is not worn or cracked and that it is seated correctly in a clean groove. Lubricate the O-ring. Reconnect the union and tighten it by hand.

Step 7

If these steps have not corrected your air bubbles, and you have an older pool pump, you may have a leak in the motor shaft seal. The picture (left) shows the location of the motor shaft seal in a cutaway version of a Hayward pump. For instructions on replacing a motor shaft seal go to our guide, How To Replace A Motor Shaft Seal.

Step 8

Another source of air leaks is the motor's drain plug on the suction side of the motor. If this plug is loose, tighten it to stop the leak.

Step 9

If you still have a significant number of air bubbles coming out of your return lines into your swimming pool, you may have a bigger problem like leaks in your underground lines. Call a pool maintenance professional to help you isolate your problem.


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Matthew  Posted: 10/3/2018 

Hello - it sounds like you have checked the o-rings thoroughly, but have you checked the glued PVC joints for a leak? Use a lit stick of incense as a marker for air leaks, by waving it near the joints while the pump is on. If there is a leak, the smoke should be sucked to the source.

Also, one of the o-rings could be watertight, but past the point of being airtight. This could lead to a very slow sucking air leak when the pump is off. If the pump system loses prime slowly after the pump is turned off, then this is probably the issue. Be sure to check the pump's drain plugs and the filter's air relief gaskets.

SoCal Pool  Posted: 10/11/2018 

You were right on the money Matthew. I replaced the o-ring on the pump lid and no more air getting into my filter. I think it's been about five years since I last replaced it, and about the same for the other o-rings, so I am going to replace them all. Thanks!!!

InyoPools Product Specialist Matt S.  Posted: 10/12/2018 

Awesome! Glad to help.

SoCal Pool  Posted: 10/3/2018 

When my pool first turns on, I see big bubbles coming into the pool through the returns. The return closest to the equipment blows the most bubbles, so much that at times water splashes up and over the coping. The bubbles diminish in size pretty quickly and after a few minutes there are no more bubbles flowing through the returns. I have noticed that, even after the bubbles have ceased, there is air in my DE filter. After bleeding the air out, no more air gets trapped into the filter while the pump is running; that is, opening the bleed valve causes water to squirt out. This has happened before and I have resolved it by cleaning the filter's o-ring and re-lubricating it. I figured gravity was pulling water level down inside the filter, after the pump has shut off, and the o-ring was allowing air to leak in. This time around, it is not resolving even though I have cleaned/lubricated the o-ring several times. The o-ring itself is not stretched and doesn't have cracks. There is no water leaking out either. I've also cleaned and lubricated the o-rings in all the valves and the pump lid. The only one I have not touched is the suction side union, as I don't see bubbles in the pump, and it seems illogical that any leak from there would end up in the filter after the pump shuts off. Is it time to replace my 25-year old filter?

InyoPools  Posted: 9/27/2018 

Hello Monty - First, it's not uncommon to see a few air bubbles at start up and it's not something to be concerned with. There would only be an issue if the bubbles persist throughout the run time of the pool pump. The guide above suggests several areas to look at on the suction side. You can also look at the pressure side of the system for any leaks while the pump is running. It's possible that when the pump turns off, that leak would draw a little air into the system.

Monty  Posted: 9/27/2018 

My pool has several bubble that come out of the return lines when the pool first turns on. It last for about ten seconds. While the pump is running it doesn't appear to suck air. The clear lid on the pump shows no air and the release valve on the filter let's no air out when opened. Where can the pool get air when off?

Matthew  Posted: 9/18/2018 

Hello, whether the bubbles are coming out of just one or all of the jets, the issue is there is air in the system. The steps for finding the cause are the same for either situation.

Old Pool  Posted: 9/16/2018 

I have bubbles coming out of only 1 of my 3 return lines in the pool. Not experience any significant water level loss. Have read posts but none I found said anything about bubbles in only one of multiple return lines. Where do I start ?

The Retired 40 y/o pool man  Posted: 9/10/2018 

One thing I did not see mentioned was melted pumps. Bad water levels, broken pipes, or forgotten lid tightening can run pump dry. I have seen the water boil inside of pumps and thus warping the pump and/or lid to where it will not seal...ever. Another thing is never lube twisted o-rings(if the o-ring itself is turned with the lid to tighten), it's OK to lube the pressed o-rings will thank me when you don't have to use a 4 foot torque bar to unscrew a pump lid.

Matthew  Posted: 8/8/2018 

Hello GG - The issue could be a bad gasket or a one of the hardware pieces of the pump is broken. But the only way to know for sure is to disassemble the pump.

GG  Posted: 8/7/2018 

Just replaced motor but when it is turned on and the basket is primed it runs fine, then the pump starts to make a clicking and squealing noise and water is coming from the pump where it is attached to the basket. could it be one of the seals. plan on taking the motor off again and checking the seal. thank you

Tom  Posted: 8/3/2018 

I keep getting air in the filter with pump. I have replaced joint at skimmer and also at pump (filter and filter line); also on pump hose and pressure hose on tank (Sequel 1 Plus) I have ran hose through 1 1/2 skimmer line and there was no blockage. When I bypassed filter there was no air leaks and plenty of pressure My pressure gauge stays at 16 to 18 lbs, it usually runs at around 12 to 14 lbs when it is running good with lots of pressure water running out I have also replaced pump and strainer (same brand) and type and everything continued to run the same I also checked the gasquet inside under the backwash control, cleaned some junk, but this also made no difference

Inyopools  Posted: 5/17/2018 

Hello Sidney - It sounds like you changed the salt level over to a Metric reading. Go to page 8 of the Aquarite Troubleshooting Manual for instructions on how to change it back.

Inyopools  Posted: 5/17/2018 

Hello Ashley - We would recommend replacing the spider gasket in your valve first. Then look for other air leaks on the suction side of the system after that.

Ashley Neidhardt  Posted: 5/11/2018 

I have a Hayward Sand filter with a multiport. i see the backwash hose is collapsed and it sucking air in thru waste port when pump is off. My super pump is not staying primed when turning the pump off and air bubble in strainer basket. I am thinking I need a new multiport valve?

Inyopools  Posted: 5/9/2018 

Hello Zach - Air is getting into your system from the suction side of the system. Check the fitting at the intake of the pump and any couplings in front of the pump. Another common place to get air is the diverter valves before the pump. There are small o-rings in those types of valves that can go bad and draw air.

zach  Posted: 5/9/2018 

I have air bubbles in 2 of 3 return jets. i thought it was ring for the lid so replaced that and still bubbles. i had to backwash and when i turned the filter back on the bubbles were gone but a few mins later they were back.

Inyopools  Posted: 5/8/2018 

Hello Dave - An underground issue would be very rare. Check the valves and couplings on the suction side of the system (before pump). It is very common to pull a lot of air through those locations. Another issue may be cavitation when you switch it to the pool skimmer. Try opening up the pool's main drain a little to allow more water into the pump.

Dave  Posted: 5/5/2018 

Hi, I have an air leak that happens when running normally, no vacuum attached. Coming into the pump I have spa suction and pool (skimmer) suction. When I close the pool side and suck through the spa, no air. When I close the spa and suck through the skimmer, lots of air. (Jandy valve). I am assuming this rules out a problem at the pump (lid, other gaskets). I have not been able to detect any pool leaks, but am worried the air is getting in underground. I have heard it can come in if the skimmer has a separation due to expansion/contraction. This is under concrete of course. Any thoughts? Thanks in advance.

INYOPools  Posted: 4/24/2018 

This sounds like an air leak on either the main drain (sump) valve or the pipe before the pipe before the valve. To address the valve, remove the valve cover so you can check that the valve cover o-ring and the diverter o-ring are not damaged. Then the next on the checklist would be to find any compromised seams in the PVC plumbing. Seams between the PVC and the valve ports, tees, elbows and any other joints should be inspected.

Paul  Posted: 4/22/2018 

Hi, When starting my in ground pool pump this spring I found it would pump water from the skimmers only. I have a pipe before the pump that splits to the skimmers and sump with a valve on each. When opening the sump valve all water disappears from the pump. When the sump valve is closed the pump primes and pumps from the skimmers. As soon as I open the valve just a tiny bit the prime drains and the pump will not pump from either.

Inyopools  Posted: 4/16/2018 

Hello Deb and Al - It sounds like you may have a significant air leak. If none of the fixes in the above guide work, check out our article titled "Why are My Pool Jets Not Working".

Deb and Al  Posted: 4/14/2018 

Hi, We are experiencing such low pressure on our pump that it is not circulating the water well at all. When it starts up in the morning, it does what it is supposed to but quickly slows to barely pushing the water and one of the jets has air bubbles.

Inyopools  Posted: 2/10/2018 

anton - I assume you have a diverter valve that lets you select water from either the main drain or the skimmer / cleaner port. If your pump loses prime in either mode, your air leak problem is not in the main drain or the skimmer / cleaner port. It would have to be in the common line going to the pump. Check the diverter valve, the connectors before the pump or the front end of the pump - the strainer cover or the drainage plugs at the bottom of the pump.. Did you change anything in any of these areas? Pull each of these area apart and check that the o-rings / gaskets are in place and the connectors are tight.

anton  Posted: 2/6/2018 

I have air bubbles coming out from the return valve in the pool. Did check the thing your other comments mentioned- for possible leaks. The system works for a few minutes then stops sucking and the pool cleaner stops. The same if I am on Backwash. It does also blow bubbles when I run the system from the bottom of the pool only? Any ideas what might cause this. Thanks for your reply.Anton

MAR  Posted: 12/19/2017 

Thank you, Inyopools for your reply. I didn't do anything else besides cleaning the basket. After reading through the comments, I ran water over the clear part of the lid and the bubbles disappeared (the bubbles don't come back after I stop running water on it) and the pump runs fine with no issues unless I remove the pump lid again. I then have to repeat this step to get the air bubbles out and everything works normal again. There are no cracks on the lid and the o-ring is new, so I have no idea why it is happening. At least I have a temporary fix till I can afford to replace the lid. Thanks for the tips.

Inyopools  Posted: 12/19/2017 

MAR - Go back to any changes you made between when it worked and the next time when it didn't. Did you change any diverter valve positions etc?. Try to see if anything you might have done affected water pressure. Then look for cracks in your strainer cover and the top of the strainer pot that the cover screws into, If diesn't take much to cause a problem.

MAR  Posted: 12/16/2017 

My pool pump is not priming fully and there are air bubbles in the strainer basket. I replaced the o-ring and the pump primed with no issue and there were no more air bubbles, but the next time I turned the pump on (after cleaning the pump basket), I experienced the same problem again. Am I tightening it too much, not tight enough? I always hand tighten. Could it be that strainer lid cover needs to be replaced or could it be something else? There are no other air leaks that I'm aware of. Thanks.

Inyopools  Posted: 11/25/2017 

Kevin - It sounds like you have a couple of issues here. Bubbles seen when the pool cleaner is on is often caused by leaks in the folds of the vacuum hose. Try pulling out a section of the hose tone at a time to see if you can identify which one is leaking. And generally speaking, you will not get air in your system from the discharge side on your pump. If you have a leak, it would squirt water not suck in air. I'm not sure what your diverter valve is doing. You might try replacing the valve assembly to see if that corrects your problem. See our guide on "How To Repair a Diverter Valve"

Kevin  Posted: 11/19/2017 

My pump is struggling to prime. Can see significant bubbles in the chlorinator and in the return jets. Only does this with pool cleaner connected. It will only prime if strainer basket filled with water. I do have a diverter (post the chlorinator) to divert to solar heater. With diverter closed (i.e. water returning directly to pool (solar heater off)) the pump will not prime sufficiently to operate chlorinator. With diverter open (i.e. solar heater on) I still get some bubbles but much less. Have checked pool cleaner pipes and strainer o-ring. It appears that air is entering at the diverter (although post-suction). Could that be possible? Help please?

Inyopools  Posted: 11/13/2017 

Tiger - It sounds like you may be getting air sucked in though your pool vacuum hose. As the hose ages, it breaks down at the connections and in the folds of the hose. Remove each section of your hose one at a time to see if that stops the air leak.

Bob Dubery  Posted: 11/2/2017 

Thanks for your advice. Water level was on the low side, but we have water restrictions in place here and so I can live with that, if the cleaner is working. And now it is. Turned out to be the where the suction line connects to the pump. I guess it was only a tiny leak because the problems would build up with time. Thanks for this site - it pointed me in the right direction.

Tiger  Posted: 11/2/2017 

Hi I just have the problem with D.E sand and dirty stuff get back into my pool immediately after I backwash the filter. It last about 30 second then stop every time I turn the pump on. I just changed all the new 8 grids 4 months ago when D.E and dirty stuff get back into my pool. After that no problems at all. Is it normal if the skimmer at the pump and the return jets have bubbles and pressure at the gauge go up and down all the time when I switch to the pool cleaning mode for running the automatic hayward pool vacuum ? But when I switch to the pool suction mode the bubbles and pressure go back to normal? Please help me to fix the problem Thank you very much for your help Tiger

auspools  Posted: 10/25/2017 

Hi, I posted a comment with regards to air in my pool line a while back, I have followed and read most tips and tricks online and still have no resolution to air in the intake line. Even despite having 2 different pool companies with trained technicians look at the issue. The air leak is from the suction side as there are groups of bubbles visible through the check valve. All my fittings, o-rings etc have been checked, smoke tested, replaced and I even had the line pressure tested up to 50kpi - all passed. However when i bypassed the intake line and ran a hose from the pool to the pump - no bubbles at all. Can anyone help here, Im thinking of now replacing the entire intake line as all the possible solutions are not providing any answers ? Could it be the skimmer ? The pool is not loosing any water. Its driving me mad as no one has a solution and the logic doesn't make sense

Inyopools  Posted: 10/24/2017 

Bob Dubery - Some of these problems, cleaner performance, pressure buildup, backward water surge, may be due to a clogged filter. If you haven't replaced your filter sand in 4-5 years, I would try that first. A tornado effect in your skimmer basket might be due to low water level or a stuck weir door only I don't know why this only happens when you disconnect the cleaner hose. I assume the cleaner hose is connected to an independent suction poet and is not hocked up through the skimmer. Check for leaks on the cleaner hose sections or connections.

Bob Dubery  Posted: 10/22/2017 

Hi, I am getting air into my pump and filter somehow. There is also a slow drop off of pressure, so my cleaner stops working. 1) The problem is worse with the cleaner connected 2) If I simply disconnect the cleaner, the motor pulls so strongly that it sets up a downward current through the cover over the leaf catcher, basket in the weir, a bit like water going down a plug hole, and sucks in air. 3) If I removed the cover over the leaf catcher basket, then there is no downwards current and no air sucked in, even if the pump runs for hours 4) There is often a surge back of air into the weir when the pump stops. 5) The pump has a sand filter. There is a build up of pressure inside the filter (but see above, only when the pump runs with the cleaner connected). If I loosen the cover through which the sand is replenished, there is a sighing sound as the pressure is released. 6) If I put the system into circulate mode (filter is bypassed, but water still circulates) there appears to be no air getting into the system and there is always good pressure for the cleaner. Can you offer suggestions as to how the air is getting in? Thanks

Inyopools  Posted: 10/13/2017 

HollywoodSquare - If you only have air when the main drain is open, it sounds like you could isolate your problem to the piping from the main drain to the diverter valve. Try putting a silicon sealant around the connector going into the valve. Then check the valve. Pull out the diverter assembly for wear. Also check the shaft O-rings and the cover O-ring. See our guide on "How To Repair a Diverter Valve".

HollywoodSquare  Posted: 10/7/2017 

I'm currently troubleshooting an air leak, this is a US Motors (fka Emerson) EUST1152 in a Hayward Super II housing, I'm almost sure it's a replacement motor. The water level is half-way up the skimmer opening, and the weir/flapper is not obstructed. Replaced the strainer basket, which was cracked, the O-ring for the strainer cover, and checked and tightened the drain plugs. Still lots of cavitation and noise under the strainer lid. I closed the valve to the main drain (with the skimmer and side-port cleaner valves unmoved), and almost immediately the strainer chamber filled with water, and practically no more cavitation or noise.

I did a smoke test around the joints from the suction lines to see if the air might be coming in there, but nothing conclusive. Unfortunately the connections are all cemented, so I can't check the unions.

Next step is to check the diffuser and impeller and motor shaft seals, but beyond that I think I have to call in a pro.

Any advice? Maybe the main drain has a clog? I live in South Florida, and Hurricane Irma dropped a bunch of debris into the pool. I'm going to try the Drain King suggestion.

InyoPools Product Specialist Dennis R.  Posted: 10/4/2017 

mike - It sounds like your main drain is clogged. Buy a "Drain King" at your local hw store and try blowing the drain pipe out from the pump end. Close off the skimmer line at the diverter valve to divert the water to the drain only.

mike  Posted: 10/1/2017 

Hello. I am having problems with my main drain. When lever is on skimmer, I get full "suction" and that works fine. However when I start to move valve towards Main, I start losing suction and if I turn to main fully, it will not draw any water except in "Spurts". The pool is 4 years old, Inground fiberglass...All connections are PVC and glued so no unions etc to try to tighten etc. Any ideas? Thank You