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 345)

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.

MRC57  Posted: 06/27/2016 8:42 AM 

I have some noticeable air bubbles in my pump basket. My return line is working fine, with no air coming out. A friend of mine had mentioned that I should have no air bubbles in the pump basket. My pressure gauge in my sand filter is around 12-14 PSI which remembering from last year is pretty normal. I have no water leaks that I can see. Should I be worrying about the air bubbles in the basket? I checked all the o-rings and everything seems to be fine. The entire set up is only 1 year old. I haven't lubed any of the o-rings yet, not sure if that will make a difference? Any advice will be much appreciated.

Inyopools  Posted: 06/26/2016 13:19 PM  Inyo Product Specialist

Robert - Try wrapping the threads of the relief valve with plumber's tape for a better seal. Also, try using shaving cream instead of a soap solution to locate suction air leaks. The leaks will be more obvious.

Robert  Posted: 06/24/2016 17:58 PM 

I definitely have an air leak but it's gotten worse in last few days. The main pump basket slowly drains (really slow but still drains overnight) when pump shuts off. I'll be doing a soap-test on lid, pipe unions, etc. I also suspect a tiny leak at the base of air relief valve. Should I be able to seal the valve base area or will I need a new relief valve? The gauge itself seems to be fine.

Inyopools  Posted: 06/20/2016 11:38 AM  Inyo Product Specialist

Fulk - I don't know what impeller backspin is. A pool motor can only spin one way by design. And where did the metal shavings from the threaded area of the impeller come from? Something wasn't working right on this new motor/impeller. And I would still spread shaving cream around the strainer lid to see exactly where the suction leak is and to show that it was not corrected by installing a new O-ring. This installer is not going to replace this motor. Get another pool man that will work with you.

Fulk  Posted: 06/17/2016 12:34 PM 

The pool guy came back out, took apart the motor and said the impeller backspun, cleaned outsome small metal shavings from the threaded area of the impeller where it goes on the shaft, put it all back together and turned it on. He absolutely will not submit for a new unit and swears the air leak is coming from the skimmer line even after i showed him the "dents" where the lid sits and told him about the hand soap getting sucket in under the lid making bubbles in the hair trap basket when i tested for a leak. Home warranty is giving us the run around along with this guy. He wants to put stop leak in the skimmer line.

Inyopools  Posted: 06/17/2016 1:05 AM  Inyo Product Specialist

Fulk - Sounds like you have a bad "new" motor. Hopefully, the pop and humming of the motor is only a failed capacitor. To see what's involved in replacing a capacitor, see our guide on "How To Replace a Pool Pump Capacitor". To verify leaks around the strainer cover, try spreading shaving cream around the edge of the cover. You will confirm better when the suction leaks are and whether or not you can fix them. From your description, you may have a damaged motor with dents around the cover seal that the O-ring won't seal. And you already know this, but you need a new pool repair man.

Fulk  Posted: 06/16/2016 21:24 PM 

So turned on the pump, heard a loud pop and now the "new" motor just hums.....

FULK  Posted: 06/16/2016 5:33 AM 

Did a hand soap "test" around the strainer lid and am pretty sure this is where the suction leak is coming from. The soap was sucked in along the edge of the lid at several different places. I shut the pump off, opened the lid and had some suds inside the basket.....I also looked and felt around the edge and there are about 3 spots that look and feel like they are dented right where the O ring and lid make contact with it...

Fulk  Posted: 06/15/2016 1:55 AM 

Pool Service guy came out, would NEVER recommend his company to anyone, very undependable. Said the motor was bad but didn't check anything else. 3 days later he replaced it. Turned it on and decided to check the impeller and said it and the brass seal were bad as well. Had to order the impellor and seal but the "new" motor ran fine. After he replaced the motor every time we shut the pump off a "burp" of water would splash out from under the hair trap lid which it never did before. There is a new O ring on the lid also. It took the guy 2 more weeks to get the parts and come back out to put them in. He threw in a handful of granular chlorine, said it should help (water was shamrock green from algae) said he had other things to do and left. Took a total of a month just to get the motor and parts replaced. Everything worked great, had 20-25psi even while vacuuming and no bubbles for 2 DAYS! Now you can hear the "new" motor making a "pulsating" sound like the old one did, strong and then weak and the pressure is flucuating again between 0-15 and bubbles are horrible in the hair trap and return jets just like before! He did not check any of the plumbing to or from the pump for leaks. We are so frustrated and don't know what else to do. I imagine there is an air leak in the plumbing above ground somewhere but am confused about the pump issue. Is it possible its a bad pump or one with a hairline crack in the cast iron?......any suggestions?

Inyopools  Posted: 06/14/2016 11:38 AM  Inyo Product Specialist

Brad - You may have leaks in your cleaner hose or its connections. Hold the sections of hose that float on the top of the pool under water. If the stops loss of prime, you have a leak in one of those sections. Take one section out at a time to isolate the leaky section. If that doesn't work, check the section of hose that is going into the skimmer for leaks. If possible, submerge the hose below the water surface at the skimmer. Make sure the skimmer bucket is full of water so that air isn't getting into the system.

Inyopools  Posted: 06/13/2016 23:34 PM  Inyo Product Specialist

Nick - See our guide on "How To Prevent DE Filter Powder Returning to Pool" for possible causes and solutions of DE going into the pool.

Inyopools  Posted: 06/13/2016 13:01 PM  Inyo Product Specialist

mpives58 - You still may be getting air sucked into your system on the suction side of your pump. A couple of thoughts. Did the tradesmen work near any of the underground suction pipes (assuming you have an in-ground pool)? Could they have loosened one of the joints? Thought two. Do you still have bubbles, if your run without the cleaner vacuum plate installed - e.g. without using the cleaner? If not, you may have a leak in one of the cleaner hoses or the plate. Is the plate completely under water? To test for a leaking hose, try holding all the hoses under water when the cleaner is operating.

Brad  Posted: 06/12/2016 16:45 PM 

Great site guys! I have a Pentair diverter to allow my inground pool to filer via the skimmer or the drain or both. When it is filtering via the drain, skimmer or both there are no issues. Only when I attempt to vacuum via the skimmer air is introduced into the pump and I loose suction. Any suggestions?

Nick  Posted: 06/11/2016 20:00 PM 

Hen my filter turns off de is backing up into pool by main drain

mpives58  Posted: 06/10/2016 18:57 PM 

I have had problem with air bubbles seen at pool pump basket for a little while. It seems to coincide with tradesmen work recently done where localised excavation and fencing was done. I had a pool man come and check the system and he changed pump suction O Rings and e pump basket O Ring seals. He said the problem was better but I still see a big drop in water level in pump basket when cleaner is fitted and air in the top of basket. Recently another pool man came and checked and said the automatic valve in line with cleaner hose and skimmer box vacuum plate was sticking shut causing too much suction at cleaner head. Once this was unstuck the cleaner works better but there is still air at the pump basket but not as much. I spoke to the pool man and asked him if I have an air leak anywhere and he said the pump may be cavitating but I don't understand what this means. I have spent money trying to fix a problem but am getting confused by the outcomes so far. What can I do?

Inyopools  Posted: 06/06/2016 10:54 AM  Inyo Product Specialist

jeff - Check your new gasket and lid first. I always go back to my last repair to resolve a problem. Then here's a link to our guide on "How to Correct Low Water Pressure in Your Pool System". It may help resolve your problem. Check for a clogged impeller first. That is a common problem with low water pressure.

jeff  Posted: 06/04/2016 6:05 AM 

replaced lid and gasket on hayward superpump after an hour or so air bubble shoes up and skimmer suction drastically decreases as does return output

Inyopools  Posted: 06/02/2016 18:08 PM  Inyo Product Specialist

Frustrated in KS - Is this an in-ground or an above ground pool. If in-ground, did you buy an above ground pool pump instead of an in-ground pump? An AG pump has to be installed below the pool to have gravity dump water into the pump. It cannot suck water up above the pool to prime the pump.

Frustrated in KS  Posted: 06/02/2016 14:23 PM 

Had to replace the pump since the old one decided it wasn't going to work when we started opening the pool. Put everything back together and now can't get it to prime. Tried all the troubleshooting techniques mentioned and can't find a leak. Could it be the pump?

Inyopools  Posted: 06/01/2016 11:54 AM  Inyo Product Specialist

Brian - It is normal in most pool systems for some of the water to drain back into the pool when the pump is shut off. It normally takes 1-2 minutes for the pump to prime when it is restarted.

Inyopools  Posted: 05/31/2016 16:28 PM  Inyo Product Specialist

Denise – You may have low water flow due to a clogged pump impeller. See our guide on "How To Clean Out a Pool Pump Impeller".

Inyopools  Posted: 05/31/2016 15:12 PM  Inyo Product Specialist

tired of failure - You are right. Air would not be coming in from the broken filter gauge. It would be squirting water. Check for the obvious suction side air leaks listed in this guide.

Brian  Posted: 05/31/2016 9:31 AM 

I noticed that when my pump is off that air gets into my motor basket and the motor loses its prime. Does this mean there is a leak somewhere?

Brian  Posted: 05/31/2016 8:44 AM 

When I start my pool pump after its been off for a while I notice that the water level in the pool motor is low and no longer primed. does this mean I have a leak somewhere?

Denise  Posted: 05/30/2016 23:22 PM 

Please tell me what I should do. Inground pool with 3 jets, and air is coming out of only 1 jet. The basket near the filter shows no air bubbles at all. When the pump is turned off, I completely lose prime. Same happens after backwashing. To get the system to fill up, I have to dump a bucket of water into the basket near the filter and then clamp down the top. What do you recommend? Thank you so much

tired of failure  Posted: 05/30/2016 9:57 AM 

My pump box is pulling in a lot of air. I noticed the sand filter gage is broken. Can this cause air to be pulled in to the pump box or would it have to be on the other side of the pump?

Inyopools  Posted: 05/30/2016 9:52 AM  Inyo Product Specialist

Randy – Sounds like you have most of the bases covered. I’d return back to the original inground suction leak to see if the repair has broken loose.

Inyopools  Posted: 05/30/2016 9:15 AM  Inyo Product Specialist

Low water at skimmer – I think you are seeing the air bubble that had collected in the system when the water was low. They should be reduced significantly after the pump has run about 5 minutes.

Randy  Posted: 05/25/2016 18:55 PM 

First off I want to say thank you for this wonderful site. So I recently had a leak detection company come out and fix an inground suction leak. The pool is working great for a few weeks but then I noticed a lot of air bubbles in the return line and in the pump basket. I replace the pump lid over ring and the plug O-rings and I do not have any unions or diverter valves before the pump. If I prime the pump and turn it off it stays primed and never loses water. But when the pump turns on even on the lowest speed it starts drawing air bubbles. Any help would be greatly appreciated thank you.