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.

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

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 (1 to 40 of 178)

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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.

User: Inyopools

Melissa - If you have opened and closed your filter without cleaning the cartridge and your pressure is still high when you start up again, you probably have a cartridge problem. It may look clean but there may be chemical residue in the folds of the cartridge that isn't rinsing out. Try soaking the cartridge in a TSP solution overnight or replace the cartridge.

User: Inyopools

Scott - If your pump is losing prime or you see a lot of air in your pump's strainer basket, you may have an air leak. Try putting a soapy solution on all the connections between the pump and the pool to see if any soap bubbles are sucked into a leak. If your pump is not losing prime, you may have back pressure building up in the filter. Many filters have a breather tube going up the center of the filter. Make sure that is not clogged.

User: Melissa

My pool filter pressure goes from 10 to 30 after I vacuum the pool. We keep cleaning it out, and that lowers the pressure, but honestly, the cartridges weren't dirty. I suspect an air leak as I have seen air bubbles in the filter basket, but can't find it. I thought opening the air relief valve on top of the filter and repricing the system would lower the pressure, but oddly enough, it didn't. Any ideas?

User: Scott "what am I missing?"

Pump is losing pressure. Here what we have done.

Relocated filter. I ran all new PVC plumbing with all brand new unions and o-rings.

Brand new multi-port.

Pump would start and we would have great pressure, but it would slow to a dribble in about 1/2 hour.

Could not get a pool tech out so they talked me through on the phone. I need a new pump.

Replaced pump and worked great for about an hour then lost pressure again. Friend told us perhaps too much sand in hayward s-filter so I removed about 30-40lbs of the 200 I put in.

Same result. I have tried everything and replaced everything. What am I missing.

Could it be air leak in the new plumbing?

User: teresa

Thank u so very much for your how to page, it was perfect. Simple so every one can under stand. Imean every one...since I am a wife of a truck driver I try to do as many of the repairs as I can so my hubby doesent have a million things to do whe he come home for 1 day.. Thank u again so much..

User: Inyopools

Russell - Sounds like your filter is clogged. If you didn't change your sand after the algae problem, I would do that now.

User: Chris

Thanks for the advice Inyopools. I corrected the problem, my pool tech was convinced it was an under ground pipe air leak. I knew it was not. It started after they replaced my pump with a new pump. It actually was my Stingl SR-500 safty vacume switch sucking in air from inside the box.. i noticed when stopping the pump with the off switch from thr Stingl box, I was hearing air realeasing from the box. It was the air hose that goes from the pump to the Stingl box...

User: Russell

We have an 18ft above ground pool. the return pressure gradually decreases and only improves after a backwash. I have to do this every other day. Pump and motor were new last summer, sand filter is 6 years old. I cannot see any air bubbles in the return water or in the pump basket. Any suggestions would be appreciated. this problem began 2 years ago and about the same time we had a mustard algae problem.

User: Inyopools

Chris - You have a suction leak somewhere between your pump and pool. Try putting a soapy water solution on all the connections between the pump and pool and check if you can see any bubbles getting sucked into a leak.

User: Chris

Just got a new hayward 1 1/2 HP pump replaced on my in ground pool, the old hayward was leaking water at the seal,& and pump was real loud. Pool was filtering fine and no air bubbles were present in filter pump skimmer or pool. Now with new pump i have air bubbles in all return jets and in pump skimmer, And with system closed down i lose prime. System operates with a Stingl vac presure monitor? I have closed main drains and bubbles still present in pump window, I have closed skimmer and bubbles still present in returns and pump window as well.

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