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.


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Inyopools  Posted: 05/23/2017 16:30 PM  Latest Inyo Product Specialist

Anonymous (AG air leaks) - There aren't many places for suction leaks between the pump and the pool, generally only the two fittings at the pool and at the pump. If these are unions, check the placement of the O-rings in the unions and tighten the unions up. If these fittings can’t be removed easily, try sealing the connections with silicon glue.

Anonymous  Posted: 05/22/2017 15:45 PM  Latest

Do you help with Above ground pool air leaks? We have actual foam that appeared on top of the pool after we opened the pool. We finally figured it out that it is due to an air leak from some visible leak. Can you guide us?

Inyopools  Posted: 05/22/2017 15:27 PM  Latest Inyo Product Specialist

islander - I don't know why the multiport valve Filter position would cause air in the pump's strainer basket. The water in the filter's multiport valve has passed the pump and shouldn't impact the pump’s operation. It shouldn't matter, but check the spider gasket in the MPV for damage. Then review this guide again for identifying air leaks.

islander  Posted: 05/20/2017 12:29 PM  Latest

When my sand filter is set to "Filter," bubbles exit the returns and air gradually accumulates under the strainer cover. Eventually, the pump no longer takes in water. When I set the filter to "Waste," the air under the strainer cover gradually decreases and the pump functions normally. So...not a suction problem, I suppose. Ideas?

Inyopools  Posted: 05/19/2017 11:01 AM  Inyo Product Specialist

Ray - See our guide on "How to Correct Low Water Pressure in Your Pool System". A clogged impeller (Step 6) is a common problem.

Inyopools  Posted: 05/19/2017 10:25 AM  Inyo Product Specialist

DD - You may have several problems. For DE powder in the pool see our guide on "How To Prevent DE Filter Powder Returning to Pool". For low water flow, see our guide on "How to Correct Low Water Pressure in Your Pool System". A clogged impeller (Step 6) is very common. For air in the return lines when vacuuming, you may have a leak in the vacuuming hose. Try holding the entire hose under water to see if the air bubbles stop. If so, you have a leak in the hose. Take a section of the hose out one at a time to isolate the leak.

Ray  Posted: 05/18/2017 5:27 AM 

I'm having problem building pressure (only got about 2 psi) Normally pool runs around 10 psi. I do have some bubbles sputtering from one of my return jets. I had to replace the spider gasket in my Hayward Vari Flow valve as that was broken. I thought this may have been the problem but it did correct it. I have also replaced the pressure gauge. Any suggestions on where to go to next?

DD  Posted: 05/17/2017 20:57 PM 

Hello, Thank you for all this helpful information. I had DE powder go back into the pool, have air coming from return lines when vacuuming, and I don't seem to have good suction from the skimmer. Are these things related?

Inyopools  Posted: 05/17/2017 10:49 AM  Inyo Product Specialist

Cmoctezu - See our guide on "How to Correct Low Water Pressure in Your Pool System". A clogged impeller is one of the most frequent low-pressure problems.

Cmoctezu  Posted: 05/16/2017 5:22 AM 

The gauge is reading 15 psi, but the water pressure feels weak compared to how it normally runs. I checked everything, clean the filter, etc., and she I first turn it on the pressure is fine, but after a bit it is weak again. However the gauge is always at 15 psi, unless it's shut off.

Inyopools  Posted: 05/15/2017 11:23 AM  Inyo Product Specialist

William - If you have a union on the discharge side of the pump, take the union apart and tighten up the pump discharge fitting. If not, you will have to cut the pipe above the discharge fitting, tighten the fitting and reconnect and glue the cut pipe. See the last half of our guide on "How To Replace a Pool Pump With An Energy Efficient Pool Pump" for cutting and gluing instructions. You only have to make one cut above the discharge fitting.

William  Posted: 05/13/2017 15:57 PM 

Oops - it's the discharge side that is leaking water at the joint with the pump. Do you have DIY guide?

William  Posted: 05/13/2017 15:55 PM 

My pump is losing prime every few seconds. I can see water bubbling from the suction side when the prime comes on. Do you have a DIY guide for replacing the leaky PVC joint at the pump?

Inyopools  Posted: 05/10/2017 10:56 AM  Inyo Product Specialist

Out of ideas - If you only have small bubbles in your returns and the pump primes fine and you have no noticeable bubbles under the strainer cover, I wouldn't be concerned. You may have a very small leak in the suction side, but it will be difficult to find.

Out of ideas  Posted: 05/08/2017 22:42 PM 

Just opened pool and got the equipment working.i am now noticing that there are small bubbles coming out of my return jets. I have a 24k gallon inground guinite pool with a cartridge pentair pump and filter. I notice that a small amount off air builds up at the top of the filter and when I bleed it out by opening the valve the air bubbles in the return temporarily stop but after 3-4 minutes return again. The pumpnprimes fine and the is no noticeable bubbles in the strainer basket. Also, I tried isolating the skimmer and main drain suction inputs to see if that had any affect. It did not.. air bubbles persist regardless of which intake the pump is drawing from. Any other ideas?? Pool is 4 years old.

Inyopools  Posted: 05/02/2017 12:10 PM  Inyo Product Specialist

Bob – I’d check any connectors on the suction side of the pump including the glued fittings (elbows, unions, valves) for suction leaks. Try brushing a soapy solution on each fitting. If the soapy bubbles are sucked into the connection, you have a suction leak.

Inyopools  Posted: 05/02/2017 11:49 AM  Inyo Product Specialist

Kpenley - Does your pool have blowback from the pump to the skimmer when you turn the pump off? If so, you probably have air building up in the top of the filter that creates back pressure against normal flow. If you have a breather hose running from the top of the tank to the bottom, make sure that hose and the screen cap are clear. Also, if you have air building up in the tank, you must have a suction side leak between the pump and the skimmer. Check the suction side fittings. I would start with the connectors to the new pump.

Inyopools  Posted: 05/01/2017 13:26 PM  Inyo Product Specialist

amada - See if your pump's impeller is clogged. See our guide on "How To Clean Out a Pool Pump Impeller". Also, if you have a breather hose going from the top of the filter tank to the bottom, make sure that hose isn't clogged.

Bob  Posted: 04/30/2017 13:20 PM 

Air bubbles are coming out of my return jets. I had a lot of air in my strainer basket until I serviced all the o rings. Now I have no air at all in the strainer but still have air in the return jets. When I shut the pump off the water drains from the strainer immediately. Are the pump/motor seals the only remaining cause?

Kpenley  Posted: 04/29/2017 19:56 PM 

I have a new pump. New sand in filter. After the pump is running for a few hours the water stops circulating. What causes this?

amada  Posted: 04/28/2017 15:59 PM 

So my problem is the following. I will tell what I have done already. The pool was dirty green and debris in it pump wasn't working. I replace pump, cleaned filter, used the dolphin to clean. It started working fine but like an hour or so later, I noticed the pressure going up and the water in the pump drainer going down. So it will work for an hour or ok, but then the same thing happens. I was told that the skimmer line might be clogged which I tried to unclogged, but still same result.

Inyopools  Posted: 04/27/2017 12:30 PM  Inyo Product Specialist

steve - No, a defective housing gasket would not cause air bubbles. The gasket is on the discharge or pressure side of the pump. It would produce a squirting water leak when the pump is on.

steve  Posted: 04/26/2017 16:08 PM 

Can a defective housing gasket cause air bubbles or will that just cause a water leak?

Inyopools  Posted: 04/21/2017 12:44 PM  Inyo Product Specialist

Dave - In in the basket area is generally due to an air leak at or before the pump. The most common pump leak is due to the strainer cover. Check the strainer cover for cracks and replace the cover if required. Then check the O-ring under the cover for damage. If it is old and stretched. I would replace it.

Dave  Posted: 04/19/2017 22:44 PM 

My pump basket has a 3-4" air gap between the lid and the water level. The pump is circulating the water well, but I can't seem to get the air out. The water also sounds like it is "sloshing" around as it goes through the heater, but not sure where to look for the air. Any ideas? Thnx.

Inyopools  Posted: 04/10/2017 12:14 PM  Inyo Product Specialist

Collette - You may have drained most of the water in your pipes to the pump. Try adding water through the pump's strainer basket for a couple of minutes to get some water back into these pipes.

Collette  Posted: 04/06/2017 15:05 PM 

Heavy rain past couple of days so I have to open the valve to release some of the water. After doing so i tried to run my pump but it won't hold the prime. I let air out of the filter but no change. Please help!

Inyopools  Posted: 04/04/2017 14:26 PM  Inyo Product Specialist

dcs - It sounds like you may have a leak in your suction cleaner hose. Try holding the entire hose under water when the cleaner is operating. If that stops the air in the basket, you have a leak in the hose or one of the hose connections.

dcs  Posted: 04/03/2017 18:40 PM 

had air in basket- water would drain out of basket when i shut the pump off, replaced all o rings water stated staying in the basket, but now there is air in it lots of bubbles when I run the pump, yet water stays in the basket-- I unhooked the pool sweep-- and the air in the basket went away and the pressure went up from 8 to twelve-- what is the problem?

Inyopools  Posted: 03/28/2017 13:49 PM  Inyo Product Specialist

rcholden - It is common for the water level to drop in the strainer basket after the pump is shut off. That's why a pump is primed - to purge the air from the system when the pump is turned back on. If you see no bubbles from the return jets or under the strainer cover after the pump has run a few minutes, your system is running correctly.

rcholden  Posted: 03/27/2017 19:38 PM 

I have NO bubbles going into the pool. The clear lid is tight and full of water with NO bubbles when the pump is running. The problem is when the pump shuts off (either with the timer or manually shut off), there are a few moments and then bubbles appear under the clear lid and then more until the water drains down to a half inch below the top of the basket that is in the container under the clear lid (sorry not good with lingo). When the pump is started, it takes a while to prime but it does prime itself. I'm certain that unless I can find the air leak, this continual priming each time the pump goes on will shorten the life of the pump. Any advice on how to approach this problem would be greatly appreciated.

Inyopools  Posted: 03/11/2017 9:45 AM  Inyo Product Specialist

Rhyno - In reading some of the forums, it sounds like many people have air trouble using a vacuum plate. When you add on the elbow onto the plate, is there a good inch of water above the elbow? Is the end of the elbow able to suck air from the surface? Try attaching a short hose full of water to the end of the elbow and feed it through the skimmer opening before attaching the hose to the elbow. Make sure the end of the hose is well below the surface of the pool. Turn pump on and see if that prevents air from getting into your system. Then attach the rest of your hose to the short hose. If that doesn't solve your problem, try buying parts to replace the vacuum plate with a direct connection to the bottom of the skimmer. See our guide to "How To Operate a Pentair Kreepy Krauly Cleaner Through a Skimmer".

Rhyno  Posted: 03/10/2017 23:30 PM 

Hi thanks for the reply ... I get air in returns and pump cavitation even without the hoses and vacuum connected. When I put the plate on top of the skimmer still OK but as soon as I conect the 90 degree attachment onto the plate for the hose to connect to is when the problem arises. I.e when suction line under load .
Thanks again for reply.

Inyopools  Posted: 03/06/2017 11:59 AM  Inyo Product Specialist

Rhyno - Sounds like your air problem is definitely with the suction port and anything attached to it. Part of the suction cleaner hose lies on top of the water. The hose may have developed leaks at the connections. Try submerging the hose below water so that everything from the cleaner to the suction port is under water. If the air bubbles stop, try isolating the leak by removing sections of the hose one at a time.

Rhyno  Posted: 03/04/2017 4:55 AM 

Hi I have quite a lot of air entering my pool via both return jets and pump cavitating. I recently installed a new system as the old one was more than 40 yrs old, in fact I replaced everything EXCEPT the suction line !!! However this problem only occurs when I plug the automatic cleaner ( Baracuda ) in . I get absolutely no bubbles when just running skimmer alone. Don't think im losing water. ( just the usual amount as is summer here and 40 degrees c plus most days) Have checked connections and water levels ok and pump is brand new. This was happening only slightly before new pump installed and is now worse. Got me pretty baffled.
Any help appreciated.
Aussie Rhyno.

Inyopools  Posted: 02/20/2017 9:32 AM  Inyo Product Specialist

Wes - If you weren't having bubbles before you changed the filter unit (pump?), I would check the connections around that unit first for air leaks. Then I would check the diverter valve for leaks. Lastly, you could have someone do a pressure test on the suction side of your piping to see if you have an underground leak. Note, if these bubbles only occur in the first few minutes on startup, you have no problem. The system is just clearing air in the system while the pump is priming.

Wes  Posted: 02/17/2017 19:06 PM 

I have a lot of air bubbles coming from the return jets at the shallow end, but hardly any from the deep end. I just had a new filter unit put in -- the old one was leaking from the lid. I have a Jandy three-way valve, and I notice when the skimmer is shut off and the main drain is left on, the bubbles persist, but when I shut off the main drain and only leave the skimmer on, the bubbles stop. Do you think I would have an underground problem or something easier? The pool's water level doesn't appear to be declining quickly; I don't know if that means anything as far as an underground problem might go. Any advice you could give I'd be grateful for. Thanks! --Wes

Inyopools  Posted: 02/13/2017 16:33 PM  Inyo Product Specialist

Roman - If your pool water is cloudy and your system is operating at 30, you should probably replace your filter. Your cartridge may look clean but after 1 or 2 years of use, the folds of the cartridge may become clogged with oils and chemicals that are difficult to remove. Most systems drain some of the water when the pump is shut off. If you have significant drainage, you may have back pressure building up in the top of your tank. Most cartridge systems have a breather tube down the center of the tank to bleed off any air that collects in the top of the tank. Make sure that tube is not clogged. Also, check for suction leaks in the lines between the pool and the input port of the pump.

Inyopools  Posted: 02/13/2017 10:03 AM  Inyo Product Specialist

WirelessDude - I would replace all the gaskets/O-rings on the suction side of the pump first. They are the easiest to correct. Then check and tighten inlet pump connection if required. Then check the skimmers for leaks where they connect to the supply pipes. If you have low water pressure, make sure the impeller in the pump is not clogged. Slight air leak at the pressure relief value, not an issue. Some people run them this way to relieve any built up air in the tank.

Roman  Posted: 02/13/2017 1:30 AM 

I have a pool with PCF 150 cartridge filter, salt chlorinator and solar heating. System is 7 years old and has worked fine until recently.
Now filter does not seem to be removing very fine particles and water remains slightly cloudy and pressure gauge doesn't get above 30 psi. When running there are no visible leaks in system. Suction pressure is v. good at skimmer. Once pump stops I can hear the filter gurgling as air enters it and the water drains out somehow. When the pump comes back on I need to open the valve at top of filter to allow air out and it seems like water has completely drained out of filter whist pump is off. I have thoroughly cleaned o-ring on lid of filter and applied small amount of silicon grease.
Would love ideas about what is causing this.