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: 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.

davidtfull  Posted: 06/06/2017 20:23 PM 

Inyopools: I do not have a salt generator or a heater. Using chlorine tablets through an inline feeder. I ran a bead of silicone around all the pvc fittings on the suction side which eliminated the small bubble (about the size of a nickel) I had in the basket. The tiny bubbles in the pool are not affecting anything, just annoying is all. Will see if sealing the pvc joints has any effect and will report back if it does. I do appreciate your prompt response to my initial concerns. Thank you.

Inyopools  Posted: 06/06/2017 16:34 PM  Inyo Product Specialist

davidtfull - Not sure what this is but it doesn't sound like these bubbles are causing any problems. If you have a Salt Chlorine Generator, it produces very, very small bubbles at the exit end of the SCG that go out through the returns.

DBoh  Posted: 06/06/2017 10:23 AM 

For my pool we use a Hayward SP2607x10 pump with an uprated 1.5HP with the proper impeller upgrade kit. For the spring opening I took a sample to the pool store and bought the recommended products. I performed the regimen as instructed (as I done plenty times now) and suddenly at the end of day 3 the pump began to whine. I pulled everything apart and the were some soft pine cone sprouts in the impeller so I cleaned and reassembled. The pump still whines but the jets seem to push as hard as before and the skimmer "seems" to vacuum okay but the pressure is much higher than normal. Any ideas? I've backwashed etc. but there at time does seem to be air in the pump. Want to verify the impeller/pump is is the issue before spending $400 for a new pump

davidtfull  Posted: 06/06/2017 2:53 AM 

I checked everything on the suction side and found no leaks. I have a very small air bubble in the strainer basket. but no bubbles coming out of the returns. Pump pressure holds steady at 15, pump holds prime, water pressure at the returns are normal, water level is correct but I still have very, very tiny air bubbles in the pool water. Very noticeable when the pool light is on. You can see tons of very tiny bubbles flowing in front of the light. When you stick your hand in the water the bubbles collect on the hair of your arms. Bubbles still remain even when the pump is turned off. What am I missing here?

Brad B  Posted: 06/06/2017 2:37 AM 

I've noticed after I backwash and return to filter mode, large amounts of air are in my return jets. Filter basket has little to no air. When pump turns off, the pressure pushes off the vacuum line and the water drains from pump. I then have to add water to filter basket in order to get it to prime. After several days, the air seems to flush from the system. But then I backwash again and the problem starts over.

It seems air is getting into the filter when I backwash - is this possible? If so, how do I prevent it?

Inyopools  Posted: 06/02/2017 13:04 PM  Inyo Product Specialist

Bob B. - The easy fixes first. Make sure your weir door is operating smoothly. Then check for a blockage in the first elbow of your skimmer using a plumber's line. If there is a blockage like a small toy that is jammed in, try opening up the diverter valve (main/skimmer and blowing the toy back to the skimmer using a Drain King attached to a garden hose. If the line is clear, you may have a broken joint where the skimmer attaches to the pipe and you may have to replace the skimmer (not easy).

Bob B.  Posted: 06/01/2017 12:08 PM 

When running pool from port 1 (skimmer to filter) there is very little suction and a lot of air in the filter basket. When pool is running on port 2 (bottom of pool), it runs perfect. I have not noticed a lower water level although we have had a lot of rain. I'm assuming there is a crack or leak in the plumbing line. Any assistance would be greatly appreciated.

Inyopools  Posted: 05/31/2017 9:58 AM  Inyo Product Specialist

wspwithe - First, try putting only 80% of a full load of DE Powder when you recharge your filter. After a backwash, 20% of the powder is left in the filter. Second, if you have an air relief tube in the center of your filter, make sure it and the screen at the top of it are not clogged. Third, does this problem occur when you have the MPV in “recirculate’ mode effectively bypassing the filter. If so, your filter is not the issue.

wspwithe  Posted: 05/29/2017 15:17 PM 

Our pool pressure has been running at 35 psi. Can't find problem. We cleaned and back washed DE filter. Turn it on, it runs at 20psi... we added DE powder...psi slowly rises...finally after about 1 hour water completely stops flowing from waterfall as if we turned it off. Definitely not filtering. Pool is green. We did remove the filter completely as well and clean it. At a loss.

Inyopools  Posted: 05/23/2017 16:30 PM  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 

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  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 

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.