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. Retape the threads of the union with two or three layers of Teflon tape and reconnect the union. Tighten the union 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.


(41 to 80 of 374)

WirelessDude  Posted: 02/05/2017 15:47 PM 

Recently cleaned and changed filters, skimmer overfilled with debris, so full that with the pump on could not pull it out. Later bubbles started on the jets, small leak on discharge pipe from pump. Have one skimmer with shut off valve, second shut off value for Main Drain and another skimmer. when I turn off main drain valve, bubbles are less but still present.
Both valves open, lots of bubbles, big drain valve closed less bubbles, skimmer valve closed, big drain open slightly less bubbles. What are the chances of two separate lines sucking air into the same pump?
Previously the pump had significant debris, at least the most I have seen because the pot basket broke when the skimmer clogged...
Thinking connections at the pump? valve o rings? gaskets in pump?
Replaced housing gasket on hayward, replaced basket gasket, system is 7 years old and the pressure release on top of tank seems not to be air tight, slight air release.

Inyopools  Posted: 02/05/2017 10:52 AM  Inyo Product Specialist

Very Puzzled - I'm puzzled too. Did the pressure test cover the whole suction side? You might have leaks around the skimmer or the cleaner hoses. A partial blockage would not introduce air into the system and you would need air to cause the air pressure buildup and backpressure after turning the pump off. Look further for air leaks on the suction side.

Inyopools  Posted: 02/05/2017 10:31 AM  Inyo Product Specialist

Blakney - I'm not sure what's going on here. This guide discusses suction air leaks that cause air bubbles in your system. Suction leaks occur before or in the pump. Your filter and multiport valve are after the pump on the pressure side of the pump and any leaks would show as squirts of water. It isn't clear from your description what your problem is. In filter mode, you may be building up air pressure in the top of the tank due to suction leaks. In recirculation mode, you would be bypassing the filter and returning straight back to the pool. This would avoid air pressure build up, but you should still see bubbles coming out of the returns.

Very Puzzled  Posted: 02/03/2017 22:59 PM 

I just had a pressure test done by a leak detector company, held 24 lbs for 10 minutes, was told no leaks. Skimmer side, no problems, vacuum side leaks enough so skimmer lid blows off when pumps goes off. driving all of us crazy. every obvious thing done, defintely only on vacuum side, could a partial blockage appear as an air leak?

Blakney  Posted: 02/03/2017 18:15 PM 

I only seem to have this problem when in filter mode. Its fine if it is in recirculation mode. Any ideas?

Inyopools  Posted: 01/09/2017 12:32 PM  Inyo Product Specialist

millbrook AL - Sometimes air pressure will build up in the top of the filter tank which will cause blow back through the pump and skimmer when the pump is turned off. Check that the air relief tube from the top of the tank to the bottom is not clogged. If the leak you have identified is on the input side of the pump, you may have found the air leak that is letting air into the top of the tank.

millbrook AL  Posted: 01/09/2017 10:10 AM 

I have an in ground pool and had a pool company come out to try and find an air leak. They said the could not find it. At the end of everyday what ever is in the skimmer ends back in the pool and sometimes the skimmer cover blows off. I have a Polaris and found small dripping leak there right before all this started. HELP

Inyopools  Posted: 12/19/2016 12:44 PM  Inyo Product Specialist

rbracer - You may have a blockage in your spa to pump line. Have someone snake or blown the line out.

rbracer  Posted: 12/15/2016 16:15 PM 

I have a pool and spa. When I turn the spa on (and close the main drain and skimmer) the water level drops in the basket and the pressure drops about 50%. Water still comes in, but never fills the basket. I cannot find any evidence of a leak around the connections (which are all glued together).

Inyopools  Posted: 11/10/2016 13:00 PM  Inyo Product Specialist

diana - If everything in your pools system seems to be working except the pressure gauge, I would question the new gauge. I know it is improbable, but sometimes you can buy a bad pressure gauge.

Inyopools  Posted: 11/08/2016 8:33 AM  Inyo Product Specialist

Air in system - It sounds like you have a suction air leak. Try applying a soapy solution around any connection on the suction side of the pump including the pump cover and input port. Watch for soap bubbles being sucked into the leak.

Anonymous  Posted: 11/07/2016 19:39 PM 

Have a new waterway pump. I can prime the pump and it runs fine but in about 5 minutes there is air in the top of the filter basket almost to the top of the suction inlet but there are no bubbles coming from the jets. The pump continues to pump water throughout the day with the trapped air in the filter basket, The only other thing I noticed is a buildup of air in the filter, which i bleed off but it builds right back up. Is this normal for this pump, any suggestions on corrective action.

diana  Posted: 11/07/2016 17:14 PM 

just had cartridges replaced in filter. Service person put in five bags of shock to get rid of algae. Now I can't get any pressure on my gauge. Replaced gauge..still not working. The pump is working air bubbles..Water circulating fine. Pump is brand new

Inyopools  Posted: 09/16/2016 12:18 PM  Inyo Product Specialist

blodg - If you see water squirting out around the pump lid when you shut the pump off, that is due to backpressure. Such a squirt indicates that you do have a leak around the lid. Check for cracks in the lid or in the basket housing around the lid. If they are sound, I would replace the O-ring even though it looks good.

blodg  Posted: 09/15/2016 15:07 PM 

That o-ring, although old and cracked, does not appear to be the problem. I tried the soap trick awa used smoke and found no suction any where around the lid (usually if that is sucking air, when the pump turns off, a squirt of water shoots out around the lid. I don't have a union in front of the basket. That only leaves the pump o-rings and the seals. What do you think?

Inyopools  Posted: 09/13/2016 22:48 PM  Inyo Product Specialist

blodg - You will not see water squirting out on suction side leaks. Any leaks before the pump will we suction leaks which such air into the system. To identify these leaks, apply a soapy solution around any connection on the suction side of the pump and watch for soap bubbles being sucked into the leak. If your pump cover o-ring is old, I would replace that first.

blodg  Posted: 09/12/2016 9:10 AM 

Earlier in the year, my filter would get air in it while the pump was running. I didn't understand it, because I didn't have a water leak. Since the pool chemistry was not being affected, I opted to wait to see if the problem progressed, and hopefully would identify the issue. Well, now the basket in front of the pump has air in it and will not pump out. I just re-greased the O-ring on that lid but nothing changed. The only thing that makes any sense is the seals in the pump as you described. But I still have no water leak!? Is that possible? I've replaced seals in pumps before, and it can be a real bear...I'd hate to do that if that can't be the problem. My pump is 20 years old and I've never replaced the seals on that pump. Thanks....great website and forum BTW.

Inyopools  Posted: 09/10/2016 16:53 PM  Inyo Product Specialist

DerfScherf - Put a soapy solution all around the diverter valve and see if any bubbles are sucked into a leak on the diverter. However, from your description of a water loss, it sounds like your problem may be with the skimmer. You may have a break in the skimmer or around base of the skimmer where it connects to the pipe. Turn your pump off and let the water setter for 10 minutes. Then put some food coloring in a straw, close the top of the straw with your finger, and place the end of the straw near the bottom of the skimmer. Then release the dye and see if it gets sucked into a leak at the skimmer connector.

DerfScherf  Posted: 09/07/2016 19:09 PM 

I forgot to add that I am losing water (approx. 3"-4" / week) I had a similar problem with the cavitation issue a few years ago and was fixed by replacing the brass gate diverter valve. Is there a way to repair the line from the skimmer without busting up all the concrete?

DerfScherf  Posted: 09/06/2016 15:59 PM 

I have a in ground pool and I think I might have a air leak on my skimmer line to the pump. I have large brass diverter valves for the skimmer and the main drain lines to the pump. If I open the skimmer valve all the way open I get air bubbles and the pump cavitates. It will only work correctly if I only open the simmer diverter valve no more than 2 turns. How do I determine if there is a problem with the diverter valve or a leak in the line?

Inyopools  Posted: 09/06/2016 9:53 AM  Inyo Product Specialist

Jojo - I'll have to think more on this one. Normally, on the discharge side, a leak would show up as a squirt - water being pushed out of the hole, not air being sucked in. But, who can argue with success?

Inyopools  Posted: 09/06/2016 9:44 AM  Inyo Product Specialist

sch - How do you know that the filter is half full when it is closed and running? What is your filter pressure gauge reading? If it is high, you may have air pressure building up in the top of the tank due to suction air leaks. If it is low, and you may have low water flow, you may have a blockage in the system before the filter. A clogged impeller is a common issue. Also, the water in the filter will drain back into the pool when the filter is open. It can only fill up completely when the system is closed.

Jojo  Posted: 09/03/2016 20:42 PM 

I just wanted to add that a worn out gasket on your chorinator lid will cause air in your returns. This is on the return side so most would not think this as possible. I know it's true because I just fixed mine after spending most of the day running down possibilities on the intake side only!

sch  Posted: 09/03/2016 19:43 PM 

I have a Hayward pup and a Stay Clear C5025 filter. My problem is my filter is only half full of water when running. I can use the bleeder and it takes just as long as after I clean my filters to bleed the air out. 10 minutes after bleeding it is half empty again. I have a good prime and my leaf basket on the pump is full and stays full. I am getting yellow algae unless I run the pump 24 7. Sometimes when I fill the filter after cleaning it drains before I put the top on. Then if I try it again it stays full.

Inyopools  Posted: 08/24/2016 9:36 AM  Inyo Product Specialist

lh - Yes, close off your skimmer intake and pull your water from the main drain. And you could add water to the intake pipes through the pump strainer basket, but the pump should prime with some air in the intake pipe without damaging the pump.

lh  Posted: 08/23/2016 18:49 PM 


Thanks for the info. I was away for a couple weeks and when I came back, the water level in the pool was very low, below the side skimmer. Adding more water is not an option right now because my water level in my well is pretty low. 2 questions:

1. While I'm waiting to have more available water to fill with, can I just switch the intake from partially side and partially bottom to only intake from the bottom of the pool?

2.Should I do something else before turning the pump back on if there is already air in there, or just let it stay on and the air will run through? Or will air running through damage the pump set-up?

Thanks for your help!

Inyopools  Posted: 07/31/2016 23:42 PM  Inyo Product Specialist

Evasport - The impeller in your Booster pump may be clogged. See our guide on "How To Clean Out a Pool Pump Impeller".

Inyopools  Posted: 07/31/2016 13:07 PM  Inyo Product Specialist

Big Bear - I do not understand your problem entirely. If you have some bubbles at the top of your pump strainer pot just under the cover, that's not uncommon. If you have significant bubbles, you have a leak somewhere in the suction line(s) between the pump and the pool. Try putting a soapy solution around the connections in the suction line(s).If you have a leak, you will see the soap bubbles moving around the point of the leak.

Evasport  Posted: 07/29/2016 21:13 PM 

I recently brought and installed a PB4 Booster pump for my inground pool.The motor works fine the shaft is turning, however I cannot get my Polaris pool cleaner to operate.Any suggestions. Also the Polaris does work. It seems that there is no pressure coming through the eye-inlet.

Big Bear  Posted: 07/28/2016 20:43 PM 

Masaic air in pump, made all normal checks, (nothing), repiped run just drain no different, new pump nothing makes any difference.

Inyopools  Posted: 07/19/2016 18:46 PM  Inyo Product Specialist

Glynn - If you only see these bubbles on startup that's all right. If they are continuous and significant, you probably have a suction air leak in your pool system between the pool and the front on of the pump. This guide covers the location of the major sources of air leaks. Try placing a soapy solution on all the connection points around the pump and between the pump and the pool. You will see some motion in the soap bubbles as they are sucked into the leak. If you have a suction cleaner, remove it and see if that eliminates the air bubbles. If so, your problem is probably in the cleaner hose.

Glynn  Posted: 07/17/2016 13:22 PM 

My water pressure gage is perfect but I'm getting air bubbles through my water outlets in the pool why is this?

Inyopools  Posted: 07/05/2016 12:39 PM  Inyo Product Specialist

jimmac - Bugs in your system and low pressure may indicate partial blockages in your pump's impeller and filter. See our guide on "How To Clean Out a Pool Pump Impeller". Clean filter.

jimmac  Posted: 07/02/2016 13:16 PM 

I have air bubbles in the pop ups and low pressure in the returns and lots of bugs coming out of one of the returns? thank you

Inyopools  Posted: 06/30/2016 18:30 PM  Inyo Product Specialist

LeeAnn - From your description. it sounds like your leak in the pool liner. If the leak was in the pipes, you would not be losing that amount of water with the pump off.

BlackhawksFan  Posted: 06/30/2016 9:26 AM 

Inyopools, thanks for the response.
I have cartridge filters, and I did try running it without the filters in. Took the psi from 20 to 18, but nothing significant. I'll try your suggestion about running a plumber's snake down the skimmer line and see if that stops the bubbles.

LeeAnn  Posted: 06/29/2016 17:20 PM 

I have a BIG leak in our in-ground pool (about 4.5 inches per day) but there is no evidence anywhere in the yard. We have no idea where the water is going. The bigger problem is that we don't know where the leak is. We have tested loss with the pool running and with the pump off to see if that would help pinpoint it. We were told that if the loss was the same the leak would be in the pool and if the loss was more with the pump running it was in the pipes. The difference was only 5/16 of an inch which is not much considering the total loss! We have looked all over the pool liner and tested as best we can with dye and cannot see where the leak could be inside. I have to decide what to tell the leak detectors to do as the fees are different and separate for diving the pool and testing the pipes and both are expensive! What do you recommend? Any other tests I should try or advice for me? Which one do I do? HELP!

Inyopools  Posted: 06/29/2016 10:30 AM  Inyo Product Specialist

BlackhawksFan - If you have a sand or DE filter, try bypassing the filter in the recirculate mode. If the bubbles stop and the flow is good, it may be time to change the filter sand or DE. If you have a cartridge filter, try running the filter without the cartridge. If that solves the issue, you may have to replace the cartridge. Over to the skimmer. You may have a partial blockage in the first elbow after the skimmer. Try running a plumber's snake through that elbow. And lastly, as the pool ages and settles, it sometimes gets cracks around the skimmer. You will probably have to have someone else look at that.

BlackhawksFan  Posted: 06/28/2016 17:34 PM 

This year I started getting bubbles from the return jets and higher than normal psi at the filter (20 vs. 12-15 normally). When I turn the valve on the suction side and close the skimmer off, the bubbles stop. I've visually checked the skimmer housing and don't see any cracks, water level is good, and the flapper isn't stuck. I'm hoping it's not an underground issue. Anything else I can check?

Inyopools  Posted: 06/28/2016 11:39 AM  Inyo Product Specialist

MRC57 - Most pumps will have some minor air bubbles in the top of the strainer basket. Based on your psi and apparently good water flow, I would conclude that your system is running well. If you want to ensure that you have no suction air leaks, try smearing shaving cream around the strainer cover and pipe connections on the suction side of the pump. Any air leaks will show up as pot holes in the shaving cream.