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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Inyopools  Posted: 02/10/2018 22:49 PM  Inyo Product Specialist

anton - I assume you have a diverter valve that lets you select water from either the main drain or the skimmer / cleaner port. If your pump loses prime in either mode, your air leak problem is not in the main drain or the skimmer / cleaner port. It would have to be in the common line going to the pump. Check the diverter valve, the connectors before the pump or the front end of the pump - the strainer cover or the drainage plugs at the bottom of the pump.. Did you change anything in any of these areas? Pull each of these area apart and check that the o-rings / gaskets are in place and the connectors are tight.

anton  Posted: 02/06/2018 11:13 AM 

I have air bubbles coming out from the return valve in the pool. Did check the thing your other comments mentioned- for possible leaks. The system works for a few minutes then stops sucking and the pool cleaner stops. The same if I am on Backwash. It does also blow bubbles when I run the system from the bottom of the pool only? Any ideas what might cause this. Thanks for your reply.Anton

MAR  Posted: 12/19/2017 17:18 PM 

Thank you, Inyopools for your reply. I didn't do anything else besides cleaning the basket. After reading through the comments, I ran water over the clear part of the lid and the bubbles disappeared (the bubbles don't come back after I stop running water on it) and the pump runs fine with no issues unless I remove the pump lid again. I then have to repeat this step to get the air bubbles out and everything works normal again. There are no cracks on the lid and the o-ring is new, so I have no idea why it is happening. At least I have a temporary fix till I can afford to replace the lid. Thanks for the tips.

Inyopools  Posted: 12/19/2017 14:10 PM  Inyo Product Specialist

MAR - Go back to any changes you made between when it worked and the next time when it didn't. Did you change any diverter valve positions etc?. Try to see if anything you might have done affected water pressure. Then look for cracks in your strainer cover and the top of the strainer pot that the cover screws into, If diesn't take much to cause a problem.

MAR  Posted: 12/16/2017 18:22 PM 

My pool pump is not priming fully and there are air bubbles in the strainer basket. I replaced the o-ring and the pump primed with no issue and there were no more air bubbles, but the next time I turned the pump on (after cleaning the pump basket), I experienced the same problem again. Am I tightening it too much, not tight enough? I always hand tighten. Could it be that strainer lid cover needs to be replaced or could it be something else? There are no other air leaks that I'm aware of. Thanks.

Inyopools  Posted: 11/25/2017 10:00 AM  Inyo Product Specialist

Kevin - It sounds like you have a couple of issues here. Bubbles seen when the pool cleaner is on is often caused by leaks in the folds of the vacuum hose. Try pulling out a section of the hose tone at a time to see if you can identify which one is leaking. And generally speaking, you will not get air in your system from the discharge side on your pump. If you have a leak, it would squirt water not suck in air. I'm not sure what your diverter valve is doing. You might try replacing the valve assembly to see if that corrects your problem. See our guide on "How To Repair a Diverter Valve"

Kevin  Posted: 11/19/2017 5:58 AM 

My pump is struggling to prime. Can see significant bubbles in the chlorinator and in the return jets. Only does this with pool cleaner connected. It will only prime if strainer basket filled with water. I do have a diverter (post the chlorinator) to divert to solar heater. With diverter closed (i.e. water returning directly to pool (solar heater off)) the pump will not prime sufficiently to operate chlorinator. With diverter open (i.e. solar heater on) I still get some bubbles but much less. Have checked pool cleaner pipes and strainer o-ring. It appears that air is entering at the diverter (although post-suction). Could that be possible? Help please?

Inyopools  Posted: 11/13/2017 9:56 AM  Inyo Product Specialist

Tiger - It sounds like you may be getting air sucked in though your pool vacuum hose. As the hose ages, it breaks down at the connections and in the folds of the hose. Remove each section of your hose one at a time to see if that stops the air leak.

Bob Dubery  Posted: 11/02/2017 23:20 PM 

Thanks for your advice. Water level was on the low side, but we have water restrictions in place here and so I can live with that, if the cleaner is working. And now it is. Turned out to be the where the suction line connects to the pump. I guess it was only a tiny leak because the problems would build up with time. Thanks for this site - it pointed me in the right direction.

Tiger  Posted: 11/02/2017 16:40 PM 

Hi I just have the problem with D.E sand and dirty stuff get back into my pool immediately after I backwash the filter. It last about 30 second then stop every time I turn the pump on. I just changed all the new 8 grids 4 months ago when D.E and dirty stuff get back into my pool. After that no problems at all. Is it normal if the skimmer at the pump and the return jets have bubbles and pressure at the gauge go up and down all the time when I switch to the pool cleaning mode for running the automatic hayward pool vacuum ? But when I switch to the pool suction mode the bubbles and pressure go back to normal? Please help me to fix the problem Thank you very much for your help Tiger

auspools  Posted: 10/25/2017 18:22 PM 

Hi, I posted a comment with regards to air in my pool line a while back, I have followed and read most tips and tricks online and still have no resolution to air in the intake line. Even despite having 2 different pool companies with trained technicians look at the issue. The air leak is from the suction side as there are groups of bubbles visible through the check valve. All my fittings, o-rings etc have been checked, smoke tested, replaced and I even had the line pressure tested up to 50kpi - all passed. However when i bypassed the intake line and ran a hose from the pool to the pump - no bubbles at all. Can anyone help here, Im thinking of now replacing the entire intake line as all the possible solutions are not providing any answers ? Could it be the skimmer ? The pool is not loosing any water. Its driving me mad as no one has a solution and the logic doesn't make sense

Inyopools  Posted: 10/24/2017 13:37 PM  Inyo Product Specialist

Bob Dubery - Some of these problems, cleaner performance, pressure buildup, backward water surge, may be due to a clogged filter. If you haven't replaced your filter sand in 4-5 years, I would try that first. A tornado effect in your skimmer basket might be due to low water level or a stuck weir door only I don't know why this only happens when you disconnect the cleaner hose. I assume the cleaner hose is connected to an independent suction poet and is not hocked up through the skimmer. Check for leaks on the cleaner hose sections or connections.

Bob Dubery  Posted: 10/22/2017 14:50 PM 

Hi, I am getting air into my pump and filter somehow. There is also a slow drop off of pressure, so my cleaner stops working. 1) The problem is worse with the cleaner connected 2) If I simply disconnect the cleaner, the motor pulls so strongly that it sets up a downward current through the cover over the leaf catcher, basket in the weir, a bit like water going down a plug hole, and sucks in air. 3) If I removed the cover over the leaf catcher basket, then there is no downwards current and no air sucked in, even if the pump runs for hours 4) There is often a surge back of air into the weir when the pump stops. 5) The pump has a sand filter. There is a build up of pressure inside the filter (but see above, only when the pump runs with the cleaner connected). If I loosen the cover through which the sand is replenished, there is a sighing sound as the pressure is released. 6) If I put the system into circulate mode (filter is bypassed, but water still circulates) there appears to be no air getting into the system and there is always good pressure for the cleaner. Can you offer suggestions as to how the air is getting in? Thanks

Inyopools  Posted: 10/13/2017 12:24 PM  Inyo Product Specialist

HollywoodSquare - If you only have air when the main drain is open, it sounds like you could isolate your problem to the piping from the main drain to the diverter valve. Try putting a silicon sealant around the connector going into the valve. Then check the valve. Pull out the diverter assembly for wear. Also check the shaft O-rings and the cover O-ring. See our guide on "How To Repair a Diverter Valve".

HollywoodSquare  Posted: 10/07/2017 19:00 PM 

I'm currently troubleshooting an air leak, this is a US Motors (fka Emerson) EUST1152 in a Hayward Super II housing, I'm almost sure it's a replacement motor. The water level is half-way up the skimmer opening, and the weir/flapper is not obstructed. Replaced the strainer basket, which was cracked, the O-ring for the strainer cover, and checked and tightened the drain plugs. Still lots of cavitation and noise under the strainer lid. I closed the valve to the main drain (with the skimmer and side-port cleaner valves unmoved), and almost immediately the strainer chamber filled with water, and practically no more cavitation or noise.

I did a smoke test around the joints from the suction lines to see if the air might be coming in there, but nothing conclusive. Unfortunately the connections are all cemented, so I can't check the unions.

Next step is to check the diffuser and impeller and motor shaft seals, but beyond that I think I have to call in a pro.

Any advice? Maybe the main drain has a clog? I live in South Florida, and Hurricane Irma dropped a bunch of debris into the pool. I'm going to try the Drain King suggestion.

Inyopools  Posted: 10/04/2017 12:06 PM  Inyo Product Specialist

mike - It sounds like your main drain is clogged. Buy a "Drain King" at your local hw store and try blowing the drain pipe out from the pump end. Close off the skimmer line at the diverter valve to divert the water to the drain only.

mike  Posted: 10/01/2017 6:43 AM 

Hello. I am having problems with my main drain. When lever is on skimmer, I get full "suction" and that works fine. However when I start to move valve towards Main, I start losing suction and if I turn to main fully, it will not draw any water except in "Spurts". The pool is 4 years old, Inground fiberglass...All connections are PVC and glued so no unions etc to try to tighten etc. Any ideas? Thank You

Inyopools  Posted: 09/19/2017 12:12 PM  Inyo Product Specialist

Andrewbic - When you re-piped everything, did that include the pipe from the skimmer to the pump, so we know there is no clog there? Can you shut off the second skimmer so you know you are only running with the good line?  Then recheck each step in this procedure to make sure each is addressed.  If that doesn't work, buy a GOKIT for your pump and replace all the gaskets/seals.

Inyopools  Posted: 09/19/2017 11:43 AM  Inyo Product Specialist

rrrod09 - I don't understand how you are seeing air in the return jets if your pump won't prime and is not moving water (or air) to the returns. If you have a priming problem, see our guide on "How To Prime a Pool Pump". Also, check that that your pump's impeller is not clogged. See our guide on "How To Clean Out a Pool Pump Impeller".

Andrewbic  Posted: 09/17/2017 18:32 PM 

Thanks. I checked the propeller and diffuser. I have pics of both Both looked well. I also used a drain king on each side of the skimmer line. I didn't see a lot of action like I expected when I ran the drain from the pump back the skimmer. I checked all Jandy valves. Even saw water running back to the pump when I ran the water from the skimmer to the pump. Finally I repiped everything and checked for leakes. So far nothing I then lubricanted the o-ring on the lid and replaced my gauge. Still the same. No suction on the skimmer side? What else could it be??

Inyopools  Posted: 09/17/2017 13:07 PM  Inyo Product Specialist

Keboss - It sounds like you may have a leak in one of your cleaner hose sections. Try holding your cleaner hose completely underwater while the pump is on to see if your pump can maintain prime. If so, pull out each section of hose one at a time to see which is leaking.

Inyopools  Posted: 09/17/2017 12:02 PM  Inyo Product Specialist

Andrewbic - When you were vacuuming all that debris, you may have clogged your pump's impeller. See our guide on "How To Clean Out a Pool Pump Impeller".

rrrod09  Posted: 09/16/2017 18:16 PM 

I have significant air in my return jets into my pool. I've primed it with no doesn't matter if I have the main drain on or the scimmer line on...any advise?

Keboss  Posted: 09/16/2017 16:34 PM 

I have an in ground pool. Everything is fine until I hook up the hose to sweep the bottom. Then I start to get air in the line and I start to lose my prime. I don't lose the prime completely unless I switch to full skimmer. Again with no hose attached in the skimmer I never lose the prime even on full skimmer. Any suggestions on my problem? My guess is I have I leak inground somewhere.

Andrewbic  Posted: 09/14/2017 20:55 PM 

After Hurricane Irma drained some water out while pulling debris and leaves out. My hope was to brush the sides and floor, vacuum, clean filter and add chemicals and fresh water. While I was vacuuming I noticed the debris was too much. I stopped and tried to start draining more and pick up debris with net. Draining was slow. Then suction from the skimmer was gone. Checked all handy valves for debris. Check both baskets. Ran a drain bladder from all ports. No clogs. Actually saw the water flowing from each point. Turned it back on and Still no suction at all. Can get flow from the main drain but not enough to fill up the cartridge tank. My focus is on getting suction back. What do you think?

Inyopools  Posted: 08/21/2017 11:15 AM  Inyo Product Specialist

Nmobae - It sounds like your motor isn't priming. See our guide on "How To Prime a Pool Pump".

Inyopools  Posted: 08/20/2017 12:57 PM  Inyo Product Specialist

Stevie70 - Is your pump not priming so you aren't able to get any water flowing through your system? If so, see our guide on "How To Prime a Pool Pump". If you have water flowing through your system but it is very weak, see our guide on "How to Correct Low Water Pressure in Your Pool System". Check for a clogged impeller first.

Nmobae  Posted: 08/19/2017 12:12 PM 

I have a pentair tagelus sand filter on my hot tub and when I checked on it this morning it was running low pressure and leaking from the fittings on either side of the motor. I tightened the fittings and the leaks stopped but now I can't get the filter to start sucking water in. Flow is zero and there is no water entering the housing before the motor. Any suggestions on issue/possible fix?

Stevie70  Posted: 08/15/2017 7:44 AM 

I have a brand new pool/cartridge filter. Air pressure is 0 psi, return water into pool has no pressure. Checked the skimmer and pump for clogging, it is not. do you turn off valve on skimmer basket? Two what else can I cjeck?

Inyopools  Posted: 08/05/2017 13:37 PM  Inyo Product Specialist

Anonymous (air in filter) - From your description, it sounds like you have a suction air leak in or before the pump. The filter is after the pump. If you had a leak in the filter, it would be a pressure leak and you would see water squirting out at that point. Suction leaks are sometimes had to find. Try blow smoke around the front of the pump and at any connection between the pump and the skimmer. If you have a suction leak, you should see the smoke being sucked into the system.

Anonymous  Posted: 08/02/2017 18:06 PM 

Hi there, I have air constantly building up in my sand filter and then coming out of my return lines in my pool, I have replaced the multi port valve, orings, checked for leaks and can't isolate the problem- it's drawing me to think it's either the sand filter or intake line.. the pump primes very well and there is no evidence of bubbles after you backwash but it builds up over a small period of time.. if it was the intake line being cracked would I be loosing water or how do I check that it's the sand filter casing me issues as my last resort is to replace the intake line ...

Inyopools  Posted: 07/31/2017 15:01 PM  Inyo Product Specialist

bere1229 - With an above ground pool, the pump is below the surface of the pool so water automatically flows to the pump by gravity. When you turn the pump on, was there a humming noise? If so, you may have a bad capacitor. See our guide on "How To Replace a Pool Pump Capacitor". Also, see our guide on "How To Troubleshoot a Pool Pump Motor - Motor Fails to Start".

Inyopools  Posted: 07/30/2017 12:31 PM  Inyo Product Specialist

Bpgraves - Sounds like you have the same problem as the previous person. Try gently blowing smoke around the front of the pump and suction side connections to see if smoke is drawn into a leak. Also, when your filter is in recirculate or backwash mode, air is not able to collect in the top of the tank as can happen in filter mode.

Inyopools  Posted: 07/30/2017 12:11 PM  Inyo Product Specialist

DE guy with pressure rise problem - When you turn off the pump, do you have a strong surge of water pushing backwards from the filter through the pump and through the skimmer. Or can you lower the psi during operation by opening the pressure relief valve to let trap air out of the top of the tank? If so, you probably have a suction air leak somewhere from the front of the pump back through to the skimmer. Try blowing smoke around the pump and connections before the pump while the pump is operating. If you have a leak, you will see the smoke being sucked into the suction side of the pump.

bere1229  Posted: 07/29/2017 21:28 PM 

I am a novice in pools. Just bought a home that came with an above ground pool and I've been trying to learn everything about maintenance and pool chemistry. Last night I came home to my 18 x 4 ft pool that had drained to about halfway. I ran to the pump and filter and saw that the hose connected from the pump to the filter had split. I had the pump running, so it was running this way for who knows how long. I bought a replacement hose and attached it, filled the pool, and connected the pump but it did not turn on. I imagine there's air in the hoses and pump basket and I don't know how to fix this. Please help! I have a Hayward pump and filter.

Inyopools  Posted: 07/28/2017 11:25 AM  Inyo Product Specialist

Pieter - It doesn't take much of an air leak to cause significant bubbles and generally these air leaks come for the suction side of your pool at or before the pump. From your description, it sounds like you may have a suction leak in your pool cleaner hose. Try holding the entire hose under water to see if that stops the increase on air in your strainer basket. If so, check for leaks in the folds of your cleaner hose or the hose connections.

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.