How to Identify and Correct Air Leaks

Written by:  Danny Rhodehamel

If you are seeing significant bubbles coming out of your return lines into the pool, you probably have an air leak in your filtration system. Possibles 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.

Tips & Warnings


Step by Step

Step 1
swimming pool filtration system

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 significant 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
pool water level

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 pint 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 tight, you may be sucking air around the lid. To check the lid, first TURN OFF POWER TO THE PUMP at the breaker box.

Step 4
pool pump strainer lid

Take off 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 may be in the goove. Check the O-ring for cracks or wear. Sometime 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. DO NOT use petroleum jelly.

Step 5
pool pump stainer lid

If your pool pump strainer lid was not the problem, check the union commonly inserted before the pump. Again make sure that 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 above, check that this O-ring is not worn of cracked and that it is seated correctly in a clean groove. Lubricate the O-ring. Retape the threads of the union with 2 or 3 layers of Teflon tape and reconnect the union. Hand tighten the union.

Step 7
pool pump motor shaft seal

If these steps have not corrected your air bubbles, and you have an older pool pump, you may have a leak in motor shaft seal. The picture at left shows the location of the motor shaft seal in a cut-away version of a Hayward pump. For instructions on replacing a motor shaft seal go to 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 significant air bubbles coming out of your return lines into your swimming pool, you may have a more major problem like leaks in your underground lines. Call a pool maintenance professional to help you isolate your problem.

Comments (41 to 80 of 228)

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User: dcvetkov

Hi There

\Trying to open a 10 year old pool, Just replaced the Whole VariFlow Xl Valve., and after few small water leaks, and fittings, now it is fine, but I have very low, pressure, barely 2 PIS, and some bubbles coming from return lines. It seems that suction is fine I cleaned the skimmer and strainer basket, and I do not see obvious source of leak., I may try to replace the O ring in the strainer basket but I think that is not the problem
Back wash line does not work also, just water does not flow through return line or waste pipe for some reason
SAnd is old about 10 years, and I dont think it has been replaced, although I used some products to chemically clean it

I think it is in the Filter is somewhere in the return lines

Water is still very dirty after super shocking the pool, maybe it is not unusual if there is no filtration for 3 days

Any advise appreciated

User: Inyopools

JSG - Glad you found your leak! Sounds like a good way to isolate the leak. However, I would recommend replacing the plumbers putty with silicone sealant as the putty is said to deteriorate the piping.

User: Inyopools

29 yr old skimmer - If your skimmer is working during filtering, it sounds like it is operational. I would question the new cleaner hose and maybe how it is installed. When the cleaner hose is inserted in the bottom of the skimmer, the skimmer should be full of water. If it drains while the hose is in the bottom of the skimmer, air will be sucked into the system. Assuming the skimmer is full of water, try pushing the cleaner hose down below the surface of the water so that everything is below water, the hose and the hose connection into the skimmer. If this works, you probably have a hole in the hose or its connections.

User: JSG

I had lots of bubbles coming out of my return jets also. There was also lots of bubbles visible under the pump strainer cover. After changing the rubber seal under the strainer cover and using liberal lubricant, still lots of air. I finally started applying a bead of plummets putty around each pic fitting on the suction side of the pump. The leak wAs one of the fittings between the jandy valve and the pump. As soon as I covered both those fittings with plumbers putty, the air bubbles were gone. I may apply some good silicone sealant if the plumbers putty doesn't last.


I have brand new pump and vacuum hose..The skimmer which the vacuum goes into is 29 years old..While filtering, there is no air bubbles in return lines..As soon as vacuum is hooked up to old skimmer, air bubbles start to come thru the return lines and shortly after I have no suction to the pool vacuum..It would seem there is a crack somewhere in the old skimmer, that is 29 years old? I am hoping not, since that will be VERY costly and can't afford right now..Any ideas how to determine if it's this built in skimmer? Thaanks

User: Inyopools

Sav - The leak in your return line would not cause air in your pump basket. That air is being sucked in on the suction side of the pump. Recheck all the connections on the piping from the pool to your pump. Sometimes when you shut off the pump, back pressure will cause water to squirt out of a suction side leak and you may be able to detect the leak that way. One other possibility: Your pump may be too large for your system causing an imbalance between the water coming into the pump and water being discharged.

User: Sav

Hello, i have air in the pump basket and tried everything to resolve the problem, but nothing worked. No difference even when i shut off the drain line or the skimmer one (i have two suction lines). I did notice though that i have a small water leak on the return line. Can this be the cause of my problem? My in-ground pool was built 3 years ago and this is the first time i am experiencing this issue.


went to lowes and spent under $4 for some pool lube and did my "0" rings on the suction side of pump. re - primed pump and it started right up with no air leaks. Freakin awesome!!!!??

User: Inyopools

Matt – It doesn’t take much of a hole to cause a suction leak. Replacing the suction hose should correct your suction side leak unless you have other leaks. Holes in the discharge side of the pump do not affect priming of the pump, but if it’s spraying water, you might as well replace it too.

User: Matt

I have a above ground pool with a less than 3 year old hayward 1.5 HP pump. I recently replaced the sand filter as it was cracked and have used this special sand instead of the regular pool sand. (i forgot what the sand is called) The sand filter i replaced was not new, and neither was the sand, but it was still in good condition. Once I hooked it up, I forgot to fill the sand filter with water, and initially the pump blew a ton of this sand back into the pool. So I went to work sucking this sand back up. Put the pump in waste only too see that It filled the entire basket in the pump with sand. This may all be concidential, because once I cleaned it out, it worked fine. Today I discovered some small pin holes on the suction side in the house from the upper skimmer to the pump. It's hard for me to believe that these small pin holes would keep the pump from working correctly. When I turn the pump off the water reverses for a second and air bubbles come out of the skimmer. From what I read I do have a air leak on the suction side, and Im hoping its only this one hose. I also have a leak in the return side. These are easy hoses to replace, I just want to confirm that 3 or 4 little pin hole leaks would cause that much pressure loss. It won't prime, water does continue to come in.

User: Inyopools

FlipJ - It sounds like your system is sucking air through the skimmer. I don't know what the "two holes on the skimmer" refers to, but in order to maintain water flow to your pump, no air can enter the skimmer bottom drain going to the pump. That well has to be continuously full when the pump is on. If you have a leak in or around the skimmer, your pump may be sucking in air through that leak. Turn the pump off and place a few drops of food coloring inside the skimmer. If you have a leak, the food coloring will seep into the leak.

User: FlipJ

We have a 35 year old pool with fairly recent equipment. Today we found the pool suction side pulling air and not filling with water. We have two inputs to the pump, spa and skimmer, and when turned to the spa side there is no problem. Turn to the pool side and starts pulling air and won't prime. We have replaced rings on the Jandy valve, cleaned the skimmer, used a water blast from both the pump and the skimmer and no solution. There are two holes on the skimmer in addition to the pump draw at the bottom, but neither seem to do anything. Any thoughts? Many thanks.

User: Inyopools

Michael - I've been thinking about this for a while and still don't have a good answer. When you went directly to "Waste" you bypassed the filter so your water flow may have been stronger. This may have dislodged a partial clog in the lines coming into the pump on the suction side. Is your pool water flow better now when you put your hand over a return? Not sure how a partial blockage would cause air bubbles unless the pump is sucking harder between the blockage and the pump thus drawing in more air at a small leak? Best I could come up with. Please let me know if someone else has a better answer.

User: Michael

I have a 22 year old in-ground pool and for the past 1 1/2 to 2 years have been plagued by constant air bubbles in the return lines. I had replaced the strainer o-ring several times, replaced the o-ring on the strained plug, replaced the three-way valve at the intake to the strained and the couplings. Nothing that I did had any affect.
I called a national pool service department who came out and looked at it and they recommended I replace the pump but wouldn't guarantee the this would fix the air bubble problem.
Typically when the pool becomes too full because of rain I use that excess water to backwash the sand filter. Done this for years since being in a drought I didn't want to waste water needlessly.
This year we've had some really good rains so rather than backwashing I set the valve to "Waste" and sent the excess directly out to the street.
IMMEDIATELY afterwards the bubbles in the return disappeared. I cannot fathom why this is but it has been a week now with absolutely no bubbles in the return lines. I'm baffled but really relieved!
I have a two speed 1.5-2.0HP pump and use high speed when running the Polaris and when using the vacuum otherwise it is on low speed 24/7.
Any idea of what was happening?

User: Inyopools

Greg - Sounds like you have covered most of the bases. The only other problem I might see is a blown underground pipe in the suction side. If it is significant, you would not be able to prime the pump to even have initial pressure. Please let me know when you find a solution so I can document it for other users.

User: Greg

Marc I have tried several repairs and checks to regain pressue in the suction line..Co2 air blast..bladder blast. replaced diffuser checked impeller ( removed and disassembled motor )replaced gaskets and seals ..removed check valve (stuck shut ) and installed straight line. checked for air leaks using smoke to detect any air going into pipe lines....cleaned DE filters and also replaced housing seal. Replaces psi pressure gauge and all fittings...I dug around skimmer and suction ( barracuda cleaner ) lines and looked for and leakage or air intake...I still have no pressure showing at psi and the barracuda crawls slow then stops after 5 to 10 minutes. what little pressure there is diminishes to 0. Any suggestions. I have had a pool company guy to the house. He has been here 4 times to assist with some of the above repairs. Greg Domet

User: Inyopools

Marc - I would have another pool man come in and check your pool system again. Sounds like the first one created a suction leak when he serviced your pool system probably around the pump. Even if your pool was operating without a suction leak, your pump may not be large enough to run the suction cleaner with all the suction pipes open. You may have to close the main drain or skimmer partially to get enough pressure to operate the suction cleaner. See our guide on "How To Set Up Pool Diverter Valves for a Basic System + Suction Port" for more information.

User: Marc

Have just bought and moved into our house which has a pool, something that we have wanted for a long time. After a couple of weeks of just my head around how to clean the pool, we got a demo suction cleaner. The pressure wasn't strong enough for it to work effectively.
We have had a guy in to see what is the issue. After cleaning filter and having pump serviced bubbles now appeared from the jets coming into the pool and the auction cleaner doesn't have enough suction to move at all.
Worried what all this may mean, how much it will cost? I hope the previous owners didn't know of any issues.

User: Inyopools

Jen - I'm not clear on the issue. When the "water goes down", is this in the pump's strainer basket? If so, with no pressure, how does the basket fill back up with water, and then repeat the cycle? Did you have this problem before you replaced the skimmer box? In any case, I don't think this is related to your old solar piping. That's on the discharge side of the pump and would show up as a spraying leak. Your issue sounds like a suction problem on the other side of the pump - water going to the pump.
It sounds like you still have a leak somewhere in the suction piping.

User: Jen

We were told by a leak detector that we had a leak at the return pipe join in the skimmer box. We have just finished replacing the skimmer box. The skimmer was around 30 years old and completely surrounded by concrete, we didn't want to have to dig it up again in the future in case of more problems. We topped up the pool and turned on the pump and filter for the first time in just under a year. The problem is the pump is fine for a few seconds and then the water drops right down and the pressure on the filter drops to almost zero till it refills with water again. The pump fills with water again then it drops. While the pool was not in use we had the solar heating removed so we could replace the roof. The solar tubing was old and ineffective so we just threw it away without replacing it. The old pipes are still in place on the side of the house and are still attached to the solar pump so is still a part of the filter and pool pump setup. Could this be the problem?

User: Inyopools

kc - If you are losing water that quickly, it sounds like you may have a major leak, and if you do not see any water spraying out around your pool equipment, the leak may be underground. The first place to check is at your return port that is making a bubbling sound. Generally you could check that by shutting off water to your return ports with a diverter valve. But, if that is your only return, you do not have that option. If you can dig behind the return port, you might try that. Otherwise you may have to bring in a professional to isolate your problem.

User: kc

Hello, I'm losing water in my pool, and the other day I went outside and was looking around my pool I heard a bubbling sound it was coming out of the return jet. I have an old pool with one jet 35x15 9ft deep. the level of the water goes down quickly and the water level is now at the level of the return jet. can you help me very concern person...kc

User: Inyopools

Zman - I'm sorry but we don't have an easy or even moderately easy solution to finding and correcting an underground leak. Check with the local pool professionals. They may have developed some cost effective approaches recently.

User: Zman

I found the jets in my spa ejecting some soil ,and spa level go down once pump stops,i think i have a leak at the underground return pipe to spa,check valve looks fine,
any recommendations how to find the leak with out digging underground the whole distance from filter to spa?
leak detectors charge an arm and leg just to find the leak,and i think they will ask for a lot to dig underground .
please help

User: Inyopools

John - I haven't seen anything like this. Sounds like some seal is failing under higher pressure, but then I can't explain why it wouldn't fail when you put 40 lbs pressure into the system. Could it be vibration? Is the pump moving around during operation? Is there a crack in the pump housing or around any of the suction fittings? You may have to have a local pool professional come in to look at this.

User: Inyopools

macpet - It is common to see air bubbles coming out of the return jets when the pump is first turned on. As the pump primes, it has to purge any air in the system that collected in the pipes while the pump was off.

User: macpet

Hi I had my pump and filer replaced in May and everything was working fine. I have now just notices when the systme starts air bubles at the return jets (both of them). Do not notice bubbles any other time. No air in any of the areas in the pump/filter system that I can see. Any suggestions? thank you

User: John

I have a Pak Fab pump. When you turn it on it will start without additional priming and fill up the strainer basket with only a small air bubble on top. It will run like this for several minutes and then as if someone opens a value it will get big burst of air in the basket and quickly lose prime. I have replaced all seals and orings. I have put pressure on the system using a drain cleaner attachment in the skimmer and I can get almost 40 lbs pressure on the system with no leaks in the pump. Any suggestions?

User: Inyopools

Air leak - First check that there are no cracks in the strainer lid or strainer bucket around the lid. Then apply a soapy solution around all the suction side connections to see if any bubbles get sucked into a leak.


air leak. change new pool pump strainer lid. still air leak form one air jet. DE filter pressure below 10. pool water level is adequate. what is next step?

User: Inyopools

Elliott - It may be that by shutting down water to your pump to only one line [skimmer] you are not supplying sufficient water to the pump. You may need to open the main drain part way to provide enough water to the pump to function properly.

User: Elliott

Hi, we are experiencing air into our pump when vacuuming the pool and putting the valve on skimmer only. Water level is ok, new hose also. I have put new sealant around the skimmer line that comes into the valve before the pump. When vacuuming, if we leave the valve selector to both the skimmer and main drain, there is no issue. Any ideas on what else to check or how to diagnose the leak? Thanks!

User: Inyopools

Michael - The first part of your comment sounds like you have a suction leak in the connections from the pool to the front end of the pump [covered in this guide]. The second part of your comment sounds like a blown spider casket in your multiport valve. See our guide on "How to Replace a Spider Gasket on a Multiport Valve".

User: Michael

Hello I have been having problems with my pump. The pump is about 3/4 full of water and there are some bubbles in the pump while running and also some bubbles coming out of the return jet. When the pump is turned off and the lid is off bubbles come from the hole on the motor side. Also when I go to backwash, water always comes out of the first filter. What is the most likely problem?

User: Randy

You are right. My tank is cracked - thanks

User: Inyopools

Randy - Check for cracks in the tank flange or the multiport flange, where the two units are clamped together. Then re-clamp the valve onto the filter tank, but as you are tightening the clamp, hit it gently with a rubber hammer all around the clamp, so it sets properly.

User: Randy

I have a hayward vari-floxl multi valve that is leaking around the o-ring between the sand filter and the valve. I replace the o-ring but it still leaked . I put silacone around the o-ring and it still leaks. Why is it still leaking?

Plesse send reply to my e-mail address.

User: Inyopools

Mike - It sounds like you have two problems; one on the suction side and one on the discharge side. Sounds like you have a suction leak. Try covering all the connections on the suction side of your pump with a soapy solution to see if any bubbles are sucked into a leak. For the main drain, shut down all suction lines to your pump except the main drain. Then use your reverse vacuum to blow out the main drain. You should see large amounts of air exiting the main drain when the main drain is clear.

User: Mike Pettis

I have a inground pool. Hayward sand filter pro series s244t. Pump loses prime after turning off and won't turn back on until I fill the basket up with water several times. Massive amount of bubbles coming out of return jet closest to the pump, zero bubbles coming out of jet furthest from the pump. Hardly any suction from skimmer furthest from the pump (which is closest to the main drain). I close the skimmers with the valve and I struggle to keep prime on my pump. Is there a way to clear the main drain? I hooked my reverse vaacum to the valve and a huge amount of water blew out of the furthest skimmer (which barely sucks water) but can't tell if it did anything to the main drain (can't tell if water is going out of it freely). ? Can you help me?

User: Nick

I found out that there was gunk at the pump impeller, pine needles, seeds, etc that made it past the basket. I had huge air bubbles from one return, no flow from the other, hardly any flow through skimmer, and hardly any water in the pump basket visible through the glass disc.

I removed the basket and reached into the port to the impeller. Lots of needles and gunk kinda stuck to the edge. Hard to get out with my fingers, needle nose pliers might be best, I had misplaced mine. I tried shop vac. If need be again, I might try the blower function from the impeller outlet after removing the hose going to the filter.

What worked this time was reached in from the basket port to the pump impeller with a screwdriver and scraping the sides. I removed 2-3 clumps of gunk. Now the returns are strong, still some small bubbles that I will bleed at the filter or replace the basket o-ring, but great flow everywhere, and major splashage in the basket.

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