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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Bpgraves  Posted: 07/26/2017 14:56 PM 

I have a problem with air in my returns. When the pump cuts off all of the water surges back into the pool. Air is getting in the system somehow. This doesn't happen when the valve is set on recirculate or backwash only in the filter mode.

DE guy with pressure rise problem  Posted: 07/26/2017 11:03 AM 

DE filter pressure rising ~10 PSI in only 4-5 hours of operations. Have been trying everything for last 6 weeks...backflushing, new DE put in, even new filter grids, thinking the old ones were microscopically plugged after TSP and acid leaks on input side of pump, breather tube filter operation, bubbles appear in strainer right ahead of pump, and water flow out of filter greatly diminishes after 4-5 hours, along with pressure rise...input seal on pump union is tight, too...have tried every trick on your website here - any other ideas?

Pieter  Posted: 07/26/2017 6:02 AM 

I installed a new pump with a new pool cleaner but still having bubbles. I do see a small leak on the filter seal can this be the cause of the bubbles? Bubbles coming out at return jet and when I open the lid to take out skimmer basket there are also bubbles? How big can the leak be to cause air bubbles? When the pool cleaner is not connected the water under the pump lid is almost to the top but when I connect the pool cleaner the water level drops to half and pool cleaner stop working? Any advice please! Thanks

Inyopools  Posted: 07/18/2017 15:47 PM  Inyo Product Specialist

Anonymous (stuck weir door) - Thank you for your feedback. I will add this solution to this guide.

Inyopools  Posted: 07/18/2017 10:41 AM  Inyo Product Specialist

Mambas - Check your cleaner hoses for leaks in the accordion folds by holding them under water or taking them out one at a time.

Inyopools  Posted: 07/18/2017 10:36 AM  Inyo Product Specialist

Sarbear - Try pulling your motor out of its housing and checking for a clogged impeller. This is a common occurrence.

Inyopools  Posted: 07/18/2017 10:33 AM  Inyo Product Specialist

Murph - Thank you very much for your feedback. It will be very useful to our customers. The stuck weir door on the skimmer has come up before. I will add it to this guide.

Inyopools  Posted: 07/18/2017 10:19 AM  Inyo Product Specialist

Anonymous (return side air leaks) – Thank you for your feedback. As you indicate, air leaks on the return side seem counter to logic. With water under pressure, you would expect a water squirt at that leak not air sucking in. But nothing speaks louder than success, and I have seen a couple of other similar comments on this subject. I'll have to research this more.

Mambas  Posted: 07/17/2017 11:06 AM 

My swimming pool pump work great until I put the kreepy krauly in. Then it sucks air all of a suddenly. What can be the cause?

Sarbear  Posted: 07/16/2017 16:09 PM 

I was vacuuming the pool and small pine ones were sucked up. The pressure dropped and the line was blocked. We ran a hose through the line and the pinecones came out. But now the pump is not getting enough pressure again. We've taken things apart and tried the seals, etc. Not sure what to do now. Was working just fine until this happened.

Anonymous  Posted: 07/16/2017 15:33 PM 

My fluctuating pressure was due to my skimmer flap being stuck in the upright position due to a poor install. I installed the flap correctly and the pressure issue went away.

Murph  Posted: 07/16/2017 10:19 AM 

Sorry, forgot to mention the "door" to the skimmer had been cemented on one side by the reconstruction people, broke it loose and solved that issue. Still have tons of bubbles.

Murph  Posted: 07/16/2017 10:11 AM 

Thank you to all.I tried the suggestions that I knew how to do, then I had a pool company come in and replace some collapsed piping in the shallow skimmer with PVC. I thought that would do it, but he left and I still have bubbles, more than I did. I have a call in for him
and I will show him this site, maybe he can help. Thanks again, I will let you know how it turns out.

Anonymous  Posted: 07/15/2017 10:14 AM 

I just resolved my problem with air bubbles in the returns. I searched for air leaks on different sites and 99% said that air leaks come only from the suction side of the pump. Not true. I did have a pvc joint leak leading to the pump which caused air bubble in the strainer basket of the pump. After fixing this issue there were no bubbles at the pump but still had air bubbles in the returns. I traced my problem to the chlorinator o-ring which had been improperly installed. Mind you, this is on the supply side of the pump. As soon as I properly seated the o-ring in the chlorinator all signs of air bubbles disappeared. Hope this helps.

Anonymous  Posted: 07/13/2017 13:56 PM 

In addition to these excellent suggestions, I have a cutoff valve on the suction side. As a last resort I replaced it. Problem solved. Works like new.

Inyopools  Posted: 07/10/2017 15:00 PM  Inyo Product Specialist

Murph - It sounds like you have a blockage in your front system between the pump and the skimmers/main drain, or you have a significant leak between the inputs and the pump. Some of this could have been from junk collected in your piping since the renovation. Look at your pump's impeller first to see if that is clogged. Then use your diverter valve to isolate the problem to the skimmers or the main drain. If you have a clog in one of these inputs, try blowing it out with an inflatable drain cleaner like Drain King.

Murph  Posted: 07/09/2017 9:29 AM 

I have a Hayward sand filter that I replaced the sand with "zeo" sand last year. My pool 20 X 40 inground pool has 2 skimmers, the shallow one will have a pipe replaced this week when the pool man gets here. It is shut off, and everything has been running fine for 3 weeks since I opened. Yesterday, I started it and 30 seconds later the pump reservoir was dry, the pump was running fine but no water was moving in the skimmer. The jandy valve directing where the water draws from was replaced last year. What else can cause the water not to draw besides a (shudder) underground leak in the deep skimmer/main drain line? I had a complete renovation done this spring, new tile, coping & plaster, could something (loose plaster, debris) have gotten in the main drain?

Inyopools  Posted: 07/03/2017 16:26 PM  Inyo Product Specialist

Faye - See our guide on "How to Correct Low Water Pressure in Your Pool System". Look at Step 6, Clogged Impeller, first. That is a common culprit.

Faye  Posted: 07/02/2017 22:26 PM 

We have changed everything on the inground pool equipment. We have a new 1.5hp motor. New arms for sandfilter and new top for sandfilter that turns for backwash,etc. (don't know technical Name). Replaced sand and we still donot have enough pressure to vacuum bottom. What could possibly be our problem? Please help!

Inyopools  Posted: 06/28/2017 10:17 AM  Inyo Product Specialist

Darrell - It sounds like you have a suction air leak that is causing air to build up in the top of the filter tank. When you press down on the MPV handle, you are opening up the system and letting this air release. Suction air leaks occur in the connections at or before the pump on the suction side of the pump between the pump and the pool. Since the MPV is on the discharge side of the pump, any leak there would show up as a squirt. So concentrate on the suction side of the pump to isolate any suction leaks. Try covering suction side connection with a soapy solution. If it has a leak, you will see soap bubbles being sucked into the hole.

Inyopools  Posted: 06/27/2017 12:53 PM  Inyo Product Specialist

drigs - Your problem sounds the same as "not a problem solver" below. See my comment to him.

Inyopools  Posted: 06/27/2017 12:47 PM  Inyo Product Specialist

not a problem solver - If you have to bleed out air from the top of your filter to increase flow, you are definitely getting air into your system from suction air leaks and this is probably causing backpressure that's impeding water flow as it builds up. Many filters have a breather tube down the center of the tank to relieve this pressure. If you have one, check to make sure it and the screen filter at the top end of it are not clogged. The suction air leaks occur at connections between the pool and the front end of the pump. If you can't see anything with a soapy solution, try using something heavier like shaving cream. A suction leak will suck the cream in leaving a pothole.

Inyopools  Posted: 06/27/2017 11:00 AM  Inyo Product Specialist

Nidhu - Since your problems seemed to start when you opened up the strainer basket to clean out debris, I would start there. Look at the strainer cover O-ring. If it is old, stretched or damaged, it may not be sealing properly. I would replace it. As for your basket overflowing, when you open up the system, water will tend to move around to find its natural level. Also, if part of your problem is low water pressure, see our guide on "How to Correct Low Water Pressure in Your Pool System". See Step 6, Clogged Impeller, in particular.

drigs  Posted: 06/26/2017 16:30 PM 

The flow out of my returns is low but the pressure is always the same as when I start it after a backwash. I cleaned the filter again today started it up and everything was fine for about an hour then the flow went down again. If I set the filter to recirculate the flow is normal. When I put it back to filter it will stay normal for about an hour again. I have a Hayward DE filter. The equipment is about 12 years old.

not a problem solver  Posted: 06/26/2017 16:07 PM 

This is our 2nd year with a pool. Older pool (30 years?). First summer, no issues. Noticed late summer that the pump was not getting great suction and flow into filter was slow. Someone finally told me to clean the cartridges . did so and everything was fine. Ran through the winter (Vegas, never froze) no issues.

About a month ago, replaced all 4 cartridges in Hayward filter. flow was great for about a day, then slowed. Then crawled, then seemingly nothing after a few weeks. Took them out and cleaned them ... same process.
This weekend cleaned them again (2 cleanings in one month!) and replaced the O-rings on the filter and on the filter lid. It is already back to seemingly no flow.

There is so little flow. I can bleed out air from the filter for about 20 seconds every day .. .it just comes back.

I have run a hose to test the flow to the holes in the pool, seems fine.
Same from the pump to the skimmer, fine.

Very few bubbles of air visible in pump basket window.

No visible water leaks in any of the exposed pipes. Have used the soapy solution, nothing that I can find.

Pump when it was working well made a noise, now it is whisper quiet.

I just want stuff to work .. that is all.

Nidhu  Posted: 06/26/2017 7:50 AM 

I have a DE filter.I see water coming out of filter basket when pump is turned off. I have two jets in the pool. One isn't doing anything and the one is majorly throwing air bubbles in the pool. This started happening after I back washed the filter and opened up the pool filter basket to take debris out. We are not really sure if this is normal for the pump basket overflowing with water when pump is off. Please advise.

Darrell  Posted: 06/25/2017 19:45 PM 

I have an issue with air in my pump. I ran a separate line from the pool directly to the pump to check if there was an issue with my underground lines- Same result. I have tried backwashing-same result. When I press down on the filter valve to relieve pressure , the pump pushes out the air and the chamber fills with water. When the filter handle is returned to normal , the air comes back. It sounds like the filter valve control is sucking air. its about 15 yrs old so maybe the seals are gone.
My heater keeps getting a low flow signal . Any thoughts?

Inyopools  Posted: 06/20/2017 11:41 AM  Inyo Product Specialist

tig - Thank you very much for your observation. The Teflon tape comment has come up before and we are trying to pull it out of our guides.

tlg  Posted: 06/20/2017 10:57 AM 

I just want to note that in step 6, you shouldn't put teflon tape on the threads of the union. The O-ring provides the water sealing. Teflon tape will only inhibit the ability to get the ring properly tightened. Also, there are mixed opinions on using teflon tape on PVC in general.

NAshvillepool  Posted: 06/18/2017 19:18 PM 

I researched this site and did a methodical, diligent step-by-step inspection of the whole routine (I'm a new pool owner with no experience; er....I'm new to pools). I found out that I had not opened one of the pipes on the suction side after backwashing. There was no reason for me to have closed it in the first place. I was just "checking systems" (ahem). The pump is fine. the water is now circulating and I have a huge job in getting the muddy Amazonian pond to look half-way respectable. I'm working on it through the stormy weather. I noticed that one the three water inlet into the pool is blowing a whole lot of air. I'm getting to that part now. Probably the gasket. Thank you.

Inyopools  Posted: 06/17/2017 12:14 PM  Inyo Product Specialist

Nashvillepool - When you say skimmer, I think you mean the strainer basket in the pump. If so, the only thing that could generate that much heat is the motor in the pump. If that is the case, I'm surprised that the motor didn't shut off before generating that much heat and I'm also surprised that all the pump's gaskets and the shaft seal weren't destroyed. With that much heat being generated, it sounds like you need a new motor.

Nashvillepool  Posted: 06/14/2017 15:56 PM 

I have a Hayward Vari-Flo XL sand filter and a Centurion switchless pump. One day recently I noticed no flow to the pool. The motor was humming and the skimmer basket was warped (melted) form the hot water. (I replaced the basket) I turned the pump off and on again a few times and I can hear a faint hiss of air a few times. I checked to see if anything was lose. I backwashed and rinsed the filter once. Then, I turned the pump on again overnight. The pumps seems to be running and I can feel the pipes vibrating/humming (as if water was running). The water is not flowing into the pool though. I kept it on though and next morning, I found the water in the skimmer hot again. I turned everything off again. What should I be looking at? Is my pump shot or am I missing something fundamanetal? Thank you!

Inyopools  Posted: 06/12/2017 18:20 PM  Inyo Product Specialist

MickeyGzzz - If you mean the piece of short pipe that screws into the pumps discharge port, it could be an adapter or a union depending on how your intend to attach the filter.

Inyopools  Posted: 06/12/2017 12:59 PM  Inyo Product Specialist

mike - You may have an air leak in your cleaner hose. Try taking all but one or two of the hoses off and see if that correct your problem. If so, you need to buy new hoses sections.

MickeyGzzz  Posted: 06/11/2017 11:05 AM 

Please if someone can tell me what the pipe that screws into the discharge side port is ? I don't know what it's name is
So thank you

mike  Posted: 06/10/2017 20:20 PM 

I recently replaced my pump and it appears to be working fine and until i plug the pool vacuum hose into the skimmer. With the vac attached the pump begins to surge and suction is greatly reduced. The water level in the strainer drops to the level where the inlet pipe is connected. It acts like the vac hose is restricted but it isn't clogged or collapsing. Does this sound like an air leak?

Inyopools  Posted: 06/09/2017 22:15 PM  Inyo Product Specialist

Thawk654 - Check that your pump's GPM water flow is smaller than your filter's capacity. Your pump may be too strong for your filter. Make sure you have the right O-ring for your MPV. As you are tightening the clamp, hit it gently with a rubber hammer around its circumference to make sure it seats properly. Check that the clamp is not bent or broken.

Inyopools  Posted: 06/08/2017 22:46 PM  Inyo Product Specialist

DBoh - It sounds like you know the difference between a full rated and uprated pump, but check again that you don't have the impeller for a 1.5 full rated pump. A full rated propeller would require your 1.5 HP pump do the work of a 2 or 2.25 HP pump and it would fail. Assuming you have the right impeller, the whining is usually an indication that the bearings are going.

Thawk654  Posted: 06/07/2017 22:23 PM 

Pressure showing 32-34psi.
Replaced the spider gasket as it was dripping water from backwash outlet.
Several days later, water started coming out of where the o-ring is. Removed multiport and replaced the o-ring with Lube Tube.
Pressure still at 32-34 and over a few hours, water begins shooting out of the clamp again.
The o-ring is "smashing" out of multiport.
I can sfigure out why this is occurring.

Inyopools  Posted: 06/07/2017 10:32 AM  Inyo Product Specialist

davidtfull - Thank you for your response. I would be very interested in your results to resolve this issue.