How to Identify and Correct Air Leaks

Written by:  Danny Rhodehamel

If you are seeing significant bubbles coming out of your return lines into the pool, you probably have an air leak in your filtration system. Possibles 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.

Tips & Warnings


Step by Step

Step 1
swimming pool filtration system

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 significant 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
pool water level

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 pint of the skimmer.

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 tight, you may be sucking air around the lid. To check the lid, first TURN OFF POWER TO THE PUMP at the breaker box.

Step 4
pool pump strainer lid

Take off 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 may be in the goove. Check the O-ring for cracks or wear. Sometime 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. DO NOT use petroleum jelly.

Step 5
pool pump stainer lid

If your pool pump strainer lid was not the problem, check the union commonly inserted before the pump. Again make sure that 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 above, check that this O-ring is not worn of cracked and that it is seated correctly in a clean groove. Lubricate the O-ring. Retape the threads of the union with 2 or 3 layers of Teflon tape and reconnect the union. Hand tighten the union.

Step 7
pool pump motor shaft seal

If these steps have not corrected your air bubbles, and you have an older pool pump, you may have a leak in motor shaft seal. The picture at left shows the location of the motor shaft seal in a cut-away version of a Hayward pump. For instructions on replacing a motor shaft seal go to How To Replace A Motor Shaft Seal.

Step 8

If you still have significant air bubbles coming out of your return lines into your swimming pool, you may have a more major problem like leaks in your underground lines. Call a pool maintenance professional to help you isolate your problem.

Comments (41 to 80 of 172)

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User: newbies

Assuming I found the air leak, how do I release the air pressure accumulated in my sand filter? Right now my system reads 20 psi when is off … how do I make that reading going down? filter backwash?? i appreciate the help

User: nibornm1

Great info and steps to follow. Thank you. In my case, I was seeing most bubbles emanating from one inlet and less in the other two. My motor and pump were just a little more noisy than usual. On disassembling the pump I found 2 small (less than 1 inch long) pieces had broken off the 14 year old filter basket and jammed in the vanes of the pump impeller. I will probably put up a photo on Youtube, user name there is nibornm1

User: Inyopools

Julius Yehilomo - It sounds like your pump is not large enough to overcome the 6.5m head of water. Also be aware that there are two kinds of pumps. The ones designed for above ground pools rely on gravity to feed the water into the pump and must be installed below the level of the pool water. You need a suction pump designed for in-ground pools.

User: Julius Yehilomo

sea water pump suction is above 6.5m from deck. It was primp 3 times but still can't suck the water from suction side.

Please need your assistance.

User: Inyopools

Air in pump - Unless you have a check valve before the pump (most systems don't) the water in you system will partially drain back into the pool from the pump and filter. It is normal for the water level in the pump strainer to drop. That's why a pump has to be re-primed each time it starts up.

User: Inyopools

matt - I don't know why shutting off the main drain line would create air in your lines unless shutting one of three lines down puts more suction pressure on the other two lines and pulls more air through a small leak. Try shutting off just the skimmer and see it that generates air also. By shutting off each line one at a time you may be able to isolate your leak to one line.

User: Inyopools

colin - Do you have a diverter valve between the skimmer and the pump? If you shut that off and the bubbles stop, you can potentially isolate your problem to the skimmer or the length of pipe between the skimmer and the diverter valve. Also check around the diverter valve for possible leaks.


I have an issue that sounds different to what most people seem to describing. When my pump is running I have no air in the system at all ( no bubbles in return jets or in the strainer basket...) But when the pump shuts down, after about 4hrs there is a lot of air visible though the clear top of the strainer basket. Where can this air be coming from if it is not entering the system while the system is running? As soon as the pump shuts down I am sure I can hear the water level dropping in the DE filter...

User: matt

i have an air leak in my system. i have three lines leading to my pump. a main drain, a vac and skimmer. when i turn on the main drain, the air leak goes away but i loose suction on my vac line (kreepy krawler weak and doesnt move). when i turn main drain off, i have air in returns with both skimmer and vac open....any thoughts.....thanks matt

User: colin

just started seeing air bubbles coming from only one jet in the pool. from the one closest to the pump. pool is not losing water. any easy way to tell if it is sucking air from the skimmer suction line that runs underground? pump lid has always a a little bit of air in the top, has no removable fittings and have not had the lid off prior to the problem starting...any ideas?

User: Inyopools

Jim P - Assuming that your jets were working and stopped - for some reason water from the pump is not getting to the jets. Do you have an automated diverter valve that controls the flow to the jets? If so, check to see if actuator on top of the valve is stuck closed and is not responding to the open signal.

User: Jim P

I have an in-ground spa/pool combo, Jandy RS6 controller for automatic controls. My spa has 6-jets, five of which blow air - one that is sucking air. I replace the whole motor assembly that generates the whirlpool action in the spa to no avail. So why is it that the 5-jets blow (and not very hard) and one-jet sucks? Please help.

User: Inyopools

Significant Air Leak – I don't know what your diverter valve set up is but look at this one to see if it’s close to what you have: “Typical Diverter Valve Setup for Pool system with a Spa”. The overview picture shows all the diverter valves for the Suction side [before the pump] and the Return side [after the pump]. Air leaks are on the Suction Side so we don't have to look at the Return valves. If you have no leaks when in Spa mode, your leak is not coming from the Spa drain line. Also the leak cannot be in the pump or pump line or you would have air being sucked in when in Spa mode. To isolate your leak open up each of the other suction lines one at a time. Review this diverter valve guide for setting instructions if necessary. First open just the vacuum liner; then just the pool drain; then just the skimmer. You may have to leave the Spa drain open with each of these tests to get enough water flow. This should isolate the problem to one of the three pool suction lines.

User: Inyopools

derek – It sounds like you may have a leak in your vacuum hose. Take the last section of your hose closest to the vacuum port [or skimmer if you are using the skimmer port] and separate it from the rest of the hose. Keep it connected to the port and hold that section of the hose completely under water. If the bubbles stop, you have a leak in the hose sections that lay on top of the water. Check each of the hose joints in the part of the hose that lays on the surface.

User: Significant Air Leak

The filtration system for our in-ground pool has a significant air leak. However, when the valves are turned for spa use, there is no air leak. I have:

1. Checked the jandy intake valve - no damage
2. Checked the skimmer/diverter valve for occlusion - clear
3. Checked for water leaks/spirts on glued connections, pump motor, lint pot lid/gasket, - none present
4. Checked with the magic 8 ball - nothing definitive

I guess I could have a breach in the intake system underground somewhere.


User: derek

I have a issue with air bubbles in my pump but only when I hook up my pool vac. When I do not use my pool vac, the system is air free. Help!


We were having bubbles every time the pump would kick on. We have an in floor cleaner and the bubbles would last for about a cycle of the pop-up heads. There was no bubbles in the pump basket but a small leak around the motor housing. We installed a new variable speed pump and but it is still popping when it kicks on. Not sure where the air is coming from. Any suggestions?

User: Inyopools

Exasperated - I would need more information on your filter to give you more specific answers. In general, first eliminate the possible effect of the cleaner by disconnecting it and running your pump without it. Then, if your filter pressure increases, you know it's not a cleaner issue. Recheck all the joints and O-rings in the pipes to the pump. When you shut off the pump and the filter has back pressure, you may see water briefly squirting out and suction pipe leaks. Correct these leaks. Then, as you pointed out, some filters have a breather tube going up the center of the filter to bleed off air collecting at the top of the filter. See if the top of that tube is clogged.

User: Exasperated

After 10 min my kreepy stops working with air in the pump strainer basket. I replaced all the Kreepy pipes, bypassed the weir-pump pipe, replaced the Kreepy, replaced the sand in the filter. It seems as though there is an increase in air pressure in the filter. Is it possible that it is the mechanism in the filter that returns air to the pool that is not functioning? How does it work and how do you check/repair it?
Thank you for your help.

User: Inyopools

SBMini - Generally when your water level falls below the skimmer, your system sucks in air causing the pump to lose prime and run dry. When that happens, the shaft seal on the motor burns up. If you fill the pool up and restart the motor at that point the shaft seal will leak, spray water on to the motor and eventually short out the motor. If you are not seeing water dripping or flowing out of the bottom of the motor, you must still have a good shaft seal. If your pump and filter are dry, I would guess that your leak started before you got home and was what lowered your pool water level to below the skimmer. Turn your pump off and try placing drops of food coloring around the bottom of the skimmer and the main drain to see if it is sucked into a leak. If you have a leak in an underground pipe, you may have to call in a professional to repair it.

User: SBMini

Our pool level got below the skimmer when we were out of town a last week. Upon returning, there is air in the system and the pressure of the filter is too high. We're going to check/replace the o-rings and the motor seal if necessary this weekend.

However, since returning we've also noticed that we're losing a lot of water. We're adding water ever day to keep it at the appropriate level. Everything around the filter and pump is dry. We aren't sure where we are losing water, but I have to think it is related to the air in the system.

It hasn't been any hotter here than normal that would explain increased evaporation either.

Any thoughts?

User: JeffS

Thanks for the helpful webpage. Just installed a new pump after my 3 year old Hayward Superjunk died. Was getting a lot of air and the solution was in your posts here. When I shut the pump off I was getting a little squirt of water from one of the drain plugs. Reseated the plug and the leak stopped. Thanks again!

User: Inyopools

Simon - A burst of bubbles out the return port on startup is normal. The pump is clearing out any air that's in the system when the pump is off. If you have algae clogging the DE surface, I would recommend backwashing your filter more frequently.

User: Simon

Upon starting pump, a strong burst of air bubbles show at the only one return port of my pool. But bubbles clear out in 10-15seconds and don't come back as long as pump is running. Does it mean I have a leaking filter tank? I suspected it because recently I had to clean the filter and replace DE every other month. Until recently I only needed clean twice a year! When cleaning filter, I notice green algae has clogged the DE surface. Is it also because air leaks into the tank when pump is idle? Thanks for any advice.

User: Long Time Pool Owner

I had tons of bubbles coming out of my jets. Nowhere on the internet did I find the solution. The problem turned out to be that my chlorinator needed a new o-ring in the cover. I wouldn't have known this except I went to add more chlorine tablets and found the old ones hadn't disintegrated much at all. I put in the new o-ring and no more bubbles!

User: Inyopools

TinyBubbles - This sounds very acceptable and nothing that you have to worry about. Most pumps have some air showing at the top of the strainer bucket. This only becomes an issue when your pump is pulling in so much air that it cannot maintain prime.

User: TinyBubbles

What quantity or amount of air in the return water is acceptable and at what point does it become a problem that must be fixed?

I definitely have a small air leak on the suction side that I cannot find. I have a two speed pump and on low speed you can actually see the tiny bubbles enter the strainer from the suction side. On high speed, bubbles swirl around the top in a small quantity but are ejected into the pool in tiny amounts as fast as they enter so air does not accumulate. The bubbles that enter the pool are very small; smaller than a BB. When the pump switches to slow speed the turbulence lessens and the bubbles in the pool stop, but the the air pocket at the top of the strainer slowly grows until tiny bubbles start to occur in the pool again and then the air level seems to remain at that point for extended periods of time as the small amount of air ingested is ejected into the pressure side.

Is this something that is acceptable for now and can be monitored to see if gets worse? Or is this a problem that needs to be addressed to prevent excessive wear on the pool pump/impeller?

User: Inyopools

Gonecrazyoverpool - The issue will be on the suction side of the pump. If you can, try closing down all but one or two of your input pipes at a time to isolate which pipe the suction leak is in. If you get prime with one or two pipes, your leak is in one of the others. Also, once you have prime, you can generally see water squirting out at the leak when you turn off the pump and get temporary backpressure. There is no device available to a homeowner that I know of to isolate underground pipe leaks. You may have to go to a professional for that.

User: Gonecrazyoverpool

Help. We r going crazy. We bought our house 3 years ago. First spring it started up ok. Second year not so much, we had the pump rebuilt. We had to run the garden hose over one of the ports on the filter until the pressure built up and then it would maintain pressure. This summer we tried sealing the unions with marine caulk as suggested. Didn't do anything. So we replaced the sand filter still wouldn't maintain pressure so we replaced the pump. We cannot get it to prime. No pressure in the system. We replaced all PVC above ground because it was dry and brittle. Still no luck. Now we r digging up the lines to see if we can see anything obvious like a bad union or hole in the lines. There doesn't appear to be anything wrong. Is there any devise we could rent to help determine where a leak is. It appears to be on the suction side because it doesn't draw water in from the pool. Help!!!!

User: Inyopools

pnc1luv - Sounds like you have two problems. Losing water when the pump is circulation water probably means you have a leak in one of your return lines and if you're getting water under the liner, it may be under your pool. The other issue is bubble in the return line. Bubbles in the returns are usually due to air being sucked in on the suction side of the pump which may mean you also have a leak in the suction side. Suction leaks do not cause water loss during operation, only bubbles in the returns. Conversely, pressure leak on the return side do not cause air bubbles - they are only squirting out water,

User: pnc1luv

Question. I'm fairly certain I have a return/pressure side leak in my plumbing of my pool. I've done this test 2x now - I leave all equipment off, for 1-2 days the water lever hardly changes. When I turn the pump on for filtration/circulation, the water level drops at a rate of about 1/4" per hour! It then also looks like water pools behind the shallow end of the pool and causes the liner to float. I have 3 return outlets in the pool, and 2 outlets on the stairs. The 3 main ones look fine, with minimum bubbles. The 2 on the stairs sounds have a LOT of bubbles coming out. Does this mean I have a leak in one of the pipes that lead to them?

User: Inyopools

jimmy - No. Bubbles in the return lines are caused by suction leaks on the suction side of the pump - water coming into the pump.

User: jimmy

Can a pressure side leak cause bubbles in the return pipe to the pool? I found 2 small leaks on the pressure side pipe to the filter right after the pump. All baskets are clean. thanks

User: Inyopools

Dominic - I had a couple of other thoughts and corrections on your problem. I misread your comment - you are using the skimmer port for your suction hose not a separate suction port. Make sure that the vacuum plate and hose connection are completely under water when you operate the cleaner and be sure to fill the hose with water before you attach it to the plate. Some systems will lose prime on just the initial air in the hose.

User: Inyopools

Dominic - If I understand you correctly, you only lose prime when the suction cleaner hose is attached to the suction port. Try two things: If you take the hose out and hold open the suction port cover, do you lose prime? If so, your leak is in the suction line. If you don't lose prime, your leak is in the hose. Try holding the entire hose under water and see if you lose prime. If not then you have a leak in the hose line that floats on the top of the water.

User: Dominic

Pool pump is fed through value with inputs from pool drain and skimmer. Prime can be maintained with valve in any position, all drain or all skimmer or anything bEtween. When vacuum hose is placed in skimmer prime is lost even with valve in mid position. New hose and vacuum plate did not solve problem. Recently had skimmer line blown as it was blocked with pine needles. This corrected flow without hose. But somehow air gets into system even though new hose.

User: Inyopools

Suibing - Had to check with the manufacturers on this one. The consensus is that you have a suction leak before or at the pump that is pushing air into the top of the filter and causing back pressure. When you change the valve setting and return back to filter, you release much of this pressure and as you return to filter, this pressure starts top build up again. Another cause of back pressure is a dirty filter, but that would not have been corrected by resetting the valve. Check any connections you recently made when you changed to new equipment. Your leak is probably in one of those connections.

User: Suibing

All settings on my above ground pool filter work great except for the filter setting. At first it works great and I have great pressure coming out of the jet but then, within a few hours, it slows to a trickle coming out of the jet. If I change the setting and then go back to filter, same thimg, great pressure coming out of the jet which then slows to a trickle. New sand, new filter and new pump. Anu ideas? Any help would be greatly appreciated.

User: wendy

My pool pump was working fine until I had backwashed it now it is sucking air and I don't know how to fix it. wendy

User: Inyopools

elaine - Fix a leak - I talked to the manufacturer on this one. He said that most people will not have the equipment to reverse the flow correctly and that you may have to have a professional do a suction leak fix.

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