How To Determine the Cause of Low Water Flow


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This guide discusses the common problems related to low water flow in your pool circulation system.

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Step by Step


Step 1

Clogged pump strainer basket - Remove the strainer basket and clean debris out with a hose.

Step 2

Clogged skimmer basket - Remove the skimmer basket and clean debris out with a hose.

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Step 3

Clogged filter - If your filter water pressure is creeping up to 10 psi above your filter's clean reading, the filter is clogging with too many contaminates and it time to clean it. Increasing pressure goes hand in hand with decreasing water flow.

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Step 4

Clogged impeller - If the pump's impeller is clogged with debris, water will not be able to flow out the side slots and generate a vacuum. Without a vacuum, the pump will not be able to suck as much water into the pump which reduces water flow. Remove the impeller and clean out the debris.

Click Here to Find Your Pool PUMP Replacement Parts (Gaskets, Baskets, Impellers & More)

Step 5

Too many features open - Are all the valves adjusted correctly? Too much equipment on at one time will stop many cleaners from working (waterfalls, spa jets, surface returns, etc.).

Step 6

Undersized impeller - When you last replaced a motor, did you match the impeller (and possibly the diffuser) to the new motor? If you put in a larger motor, you may have an undersized impeller.

Click Here to Find Your Pool PUMP Replacement Parts (Gaskets, Baskets, Impellers & More) 

Step 7

Air leak in suction side - A suction leak will reduce the vacuum generated in the pump which will reduce water flow and possibly lead to lose of priming in the pump.

Step 8

Water leak in the pressure side of the pump - A pressure leak will cause lose of water and water pressure in the circulation lines between the pump and the pool return ports. Generally these leaks can be corrected by replacing a bad gasket in the pool equipment after the pump.

Step 9

Pump too small - The pump suction cannot overcome the total dynamic head (line resistance) in your pool circulation system.

Step 10

Underground leak - If you have an underground leak, you can dig up some of the lines yourself. However, for generally less than $100 to $200 you can have a professional come in with special detection equipment that will pinpoint your leak including areas under the pool that you can't get to. Costs to repair the leak will vary according to where it is.


(1 to 40 of 55)

 Posted: 8/11/2021 

Hello - we are new pool owners. Inground 10,000 gal pool, variable speed pump, DE filter. All new this year. The other day our return had very little flow and the pool was dirty and starting to have algae so we cleaned the filter and replaced the DE even though the filter PSI hadn't changed much. That helped a lot and water cleared. That was Friday, now on Tuesday I notice the same thing. The pump primes fine and seems to be working fine, but I can tell there is little flow from the filter on. Surely it didn't fill up with dirt that quickly that it needs cleaned again after only 4 days? Any input is appreciated.

InyoPools Product Specialist  Posted: 8/11/2021 

If your water is turning green, that means there is no chlorine in the pool. So, once you got the filter clean, and I presume you shocked the water, that algae begin to die. The green algae then die, which makes it go to a hazy white color. Unfortunately, that dead alga doesn't disappear, it rightfully gets trapped in the filter, and you need to repeatedly clean and backwash the filter until the haziness is gone. If you do not keep a consistent level of chlorine in the water this cycle is going to repeat itself.

 Posted: 10/12/2017 

I have a 40000 gallon indoor pool that was working great running a Hayward Whisperflo 1.5 HP energy efficient pump, DE filter (60) with an automatic pool cleaner and solar heat. The suction and output flow was very good and powerful. My local pool store convinced me to switch to a store installed 3 HP Hayward variable speed pump, and a salt system for chlorine generation to save money. Immediately after the install, suction and flow was drastically reduced. Installation changes to the system included most of the above ground lines. Visible changes include shortened distance from the pump, more bends on the suction side to the filter, air in the pump, water leaks at the salt cell (too large a gap to fully thread) air bubbles in the flow back into the pool. At 3000 or 3600 rpm which is part of the prime, the pool cleaner line will be kicked out, yet the suction is almost non existent with poor flow and circulation. The pressure at the DE filter was 10-15 PSI (without and with the filter and DE) before the new install and is 22-30 at 3000 rpm (and higher at 3600 rpm-full power). Trouble shooting by the pool supply guy consisted of removing the DE filter and running the canister empty, bleeding airbuild up, and disconnecting the automatic pool cleaner, which would not move due to the low suction, to reduce bubbles. However, the bubbles were still there, and the pressure was still high with minimal suction and flow. He did not check for leaks. He then told me to get a new suction pool cleaner, to keep the filter clean, and that the higher pressure at the filter and the kick-out at the skimmer, is normal because it is a higher HP motor. I got a new suction pool cleaner, no go. Got lower flow suction pool cleaner, no go (and 15% restock),.Filter is clean. Performed the jmpeller check. I am planning to redo the plumbing as the next step due to all the leaks. Are there any other possible causes(such as number of 90 degree bends something got stuck in a line)?

InyoPools Product Specialist  Posted: 9/27/2017 

Kim - You might have to bring your pool guy back to snake out the return pipe. But, before you do, check for a clogged impeller and check your filter. If you have a cartridge filter it might be clogged with oils and chemicals and might need to be replaced. If you have a sand filter and haven't replaced the sand in 5 years, consider replacing it.

 Posted: 9/26/2017 

Hi! I'm hoping you can give me guidance. I have a 10000 gal pool that was having issues with suction. I had my pool guy came by to snake the pipe. He snaked through the pipe that was auctioning the water in and got some leaves out. Now it's giving me great suction but the return is very weak. I'm wondering if he had to snake through the pipe where the water was returning?

InyoPools Product Specialist  Posted: 8/23/2017 

george - I just talked to a filter manf expect and he said your problem is probably due to old sand. With use, the sharp sand edges wear down and become round. This allows the sand to pack down tighter to the point where it will block the flow of water through it. When you lift the sand during backwash, it creates temporary air pockets which collapse during the initial filter operation. He suggests that you replace your sand.

 Posted: 8/22/2017 

Hello All, I have a problem with my pool filter, the return is very slow but the pressure is reading about 17 PSI, I cleaned the filters many times when I start the filter the return is strong but keeps decreasing until it gets to a point there nothing coming back from the filter, this happens within 45 min to an hour after I cleaned the filter, what do you think is the problem?



InyoPools Product Specialist  Posted: 8/15/2017 

vicky - If you are having minimal or no water coming through your skimmer pipe when you use the drain de-clogger, it sounds like you have a blockage in that pipe like a small toy. Try snaking a thin electrician's fish tape into the pipe to see if you can pass it all the way through. Or try it from both ends. If you can't get it through, you have a blockage probably near the skimmer end at the piping's first or second elbow. Ask your local pool store if they could get it out.

 Posted: 8/12/2017 

Hoping someone can help, i have been at this for 4 days and i can't figure it out. I have a 10000 gallon inground pool, with a hayward filter. We started losing pressure about a week ago, i found the grids to be completely caked with DE, i cleaned all grids, lubed all gaskets and it started up great, started vacuuming, it lasted for about 15 minutes. i had no pressure and very little suction in the pool skimmer. I checked for air leaks, re piped the "suction" side of the pump, replaced all o-rings and lubed them. I also tried to flush the lines with that plumber thing (attaches to the hose, expands and uses pressure)when i put it in the pump skimmer side, some water comes out of the pool skimmer, however if i put it in the pool skimmer, no water comes out of the pump skimmer. there is suction but very very minimal, lots of bubbles on the return end. when i start up the filter, the air release valve does not have a constant stream but intermittent stream. i am at my wits end and can't figure this out. can't afford to call in the professionals right now. Can anyone think of anything i may have missed, any suggestions as to what else i can try to remedy this? i just need it to filter.
thank you so much in advance


InyoPools Product Specialist  Posted: 8/5/2017 

Anonymous (no water flow) - If you have no water flow at all, see our guide on "How To Prime a Pool Pump". If you have flow but it is low, see our guide on "How to Correct Low Water Pressure in Your Pool System". Check for a clogged impeller first.

Anonymous  Posted: 8/2/2017 

Have tried everything, cannot get water to flow

InyoPools Product Specialist  Posted: 7/31/2017 

JB - I'm surprised your pool didn't drain more. Sounds like the pump must have shut off after a short time in Backwash?? For low flow, check to see if your pump's impeller is clogged.

 Posted: 7/29/2017 

Accidentally forgot and left backwash on over night. Pool was still full, but now the pump and filter don't have much water flow and 0 pressure.

InyoPools Product Specialist  Posted: 7/24/2017 

JohnT - If the pump is running loud, it's motor probably needs to be replaced. And if it ran dry for a length of time, the shaft seal and gaskets may have been damaged. You wouldn't need to replace the whole pump, just the motor and gaskets.

 Posted: 7/20/2017 

I have low pressure on my sand filter I am gonna backwash in the am
But I was out of town and I'm not sure if my house sitter turned of my pump for 3 days? Now my pump is louder and reading 10 psi but I cleaned out skimmer basket and filter basket but still looks like air is getting in. Returns are blowing decent no air bubbles but I'm sure it's a gasket. My question is that I have an autovacuum and my wife just did landscaping Is my breather valve somewhere between my skimmer and my pump? Did or could she have clogged it while pulling out plants? First time pool and home owner just really need help I can't afford all new pumps and lines. Please help!!


InyoPools Product Specialist  Posted: 7/1/2017 

DavicD - Do you feed the vacuum hose into the skimmer and then lose prime in the pump shortly after? Is the end of the hose in the skimmer covered with water so your system is not sucking air? It sounds like air is getting into the system with the vacuum hose inserted.

 Posted: 6/30/2017 

Above ground pool. May have multiple problems.

When the pump was turned off the skimmer was backing up so there was obviously some pressure buildup in the tank from a leak.

I replaced the hose from the skimmer to the pump and that problem seems to be gone. The normal pressure went up to 26 from around 20 earlier.

I have good flow on the return with no bubbles since replacing the hose above. The flow at the pump filter basket is virtually solid water against the clear top.


Since long ago I have been getting useless vacuum force, just a trickle in the pump filter basket and minimal return flow shortly after attaching the primed vacuum hose. This has not improved today.

The hose does not appear to be blocked as I prime it with the return pressure and would blow out any blockages.

I've also filled the vacuum hose with water and left it out of the pool. It retains the water.



InyoPools Product Specialist  Posted: 6/24/2017 

john - Don't know why you would have good flow in the pool and not in the spa unless you have a diverter valve that is closing off flow to the spa or you have a blockage in the primary spa return pipe. For general low water flow, check your pump's impeller to make sure it is not clogged. See our guide on "How To Clean Out a Pool Pump Impeller".

 Posted: 6/22/2017 

My psi reading is fairly normal at 10 psi and their are no air leaks (bubbles) at the skimmer basket (although there was a recent crack in the skimmer base which i fixed with pvc glue/cement), my main pool return is flowing great but my spa return jets have no flow. i also keep getting algae buildup every couple of days. Suggestions?

InyoPools Product Specialist  Posted: 6/17/2017 

Van - When you shut off the pump, is there an immediate backpressure surge or water from the filter through the pump and out the skimmer. If so, you may have air pressure building up in the top of your filter that is impeding the flow of water. This buildup is due to suction air leaks in the system between the pump and the skimmer. See our guide on "How to Identify and Correct Air Leaks" to eliminate these suction air leaks.

 Posted: 6/14/2017 

Hi, you asked if flow slows down in re- circulate mode. No it does not, actually runs great , flow is strong . It's only in filter mode that psi rises and flow to return all but stops after a few hours. I have changed sand, laterals, pump and multivalve port. Still does the same thing. Psi starts at 17 and goes to 22 within a few hours and flow slows to non existent. Thhanks

InyoPools Product Specialist  Posted: 6/13/2017 

Anonymous (Low water flow) - Generally, when you initially have strong water flow and it becomes weak in a short period of time, it is because of a buildup of backpressure in the top of the filter tank. This buildup is due to air entering the system through suction air leaks at or before the pump. See our guide on "How to Identify and Correct Air Leaks".

 Posted: 6/12/2017 

Good evening.

We are first time homeowners and have had the chance to experience having our very first pool as well. We had our pool opened in April and have yet to be able to utilize it. Our pool is a 12,000 gallon salt water pool. The pump and pool equipment sit up and away from the pool on an incline. The pump/motor is a waterway SVL56 and seems to be running great. Our issue is this:
The pool has a flap/valve that is in place to prevent back flow of the water if the pump shuts off. This valve is not wanting to stay up because we seem to be losing suction after a little while of the pump being turned on. The pump will prime beautifully when we have it on the waste line with incredible suction through the skimmer. When on the waste line, the flap/valve is at a 90 degree angle allowing excellent flow. When we switch the pump to the skimmer and off of the waste line, the valve drops and then only recovers about halfway. We have decent suction through the skimmer for a bit and then we lose almost all suction and have minimal flow of water through our jets. If we switch back to the waste line, the suction is back at 100%.
We have had two pool companies out and both of them seem baffled by this issue. Apparently none of the issues add up to a fixable solution and we have no idea what to do now. They have verified no air leaks around the pump, the skimmer basket is clear and we are free of debris and clogs anywhere one could be. The line has been purged, the motor has been given the all clear, the pressure gauge has been changed, o-rings all look great.. At this point we are just paying people to come tell us they have no idea what the issue is. They have mentioned a possible crack or air leak in a pipe that we cannot see, however, how does that work when we have phenomenal suction when we are on the waste line? The water is still coming from the same pipes when on waste as it is when it's on the skimmer, correct? Does any of this sound a familiar


 Posted: 6/12/2017 

We just installed a new pump sand filter pump on our pool it's a 15 foot by 30 ft pool 54 in deep and the pump whenever we place the pump setting on filter leaks water through the hose until we turn it off we have to constantly leave it on waste but it's not filtering what should I do. I have to leave settings on waste all the time so I don't list my pool water. Please email me at acropmarbl at a o l dot c o m

Anonymous  Posted: 6/12/2017 

I have a Hayward cartriage filter when I first start the filter the water return us strong after about five minutes it comes out very weak any tips what is wrong?

InyoPools Product Specialist  Posted: 6/11/2017 

Rob1 - All that seems to be left is a significant suction air leak in the skimmer line. Do you see any bubbles coming out of the returns when the skimmer line only is open? Check around the base of the skimmer for a crack.

 Posted: 6/9/2017 

Algae took over my pool in the spring. I remember right before I started treating the pool that the jets would quickly go from working to nothing. I started treating the water and got ready to vacuum it (leaves also at the bottom) on waste, but I barely have any flow out when the main drain is closed leaving only the skimmer open for vacuuming. I opened back up the main drain while on waste and I then again have the full flow out onto the street. We used a bladder to close off and force water back from the pump basket to the skimmer with main drain turned off. Water will flow either way and we didn't really see where a blockage was removed. Still very low flow from just skimmer on waste. Any suggestions????? I can't vacuum pool without more suction.

InyoPools Product Specialist  Posted: 6/8/2017 

VVan - Do you have reduced flow when you run in "Recirculate" mode - bypassing the filter? If so, your problem is outside your filter. When you shut off the pump, is there an immediate backpressure surge or water from the filter through the pump and out the skimmer. If so, you may have air pressure building up in the top of your filter that is impeding the flow of water. This buildup is due to suction air leaks in the system between the pump and the skimmer. See our guide on "How to Identify and Correct Air Leaks" to eliminate these suction air leaks.

 Posted: 6/6/2017 

Hi, flow starts out fine and within a few hours is drastically reduced. Changed the sand (same thing happens) bought a new pump, same size as old one ( same thing happens) took apart plumbing from filter to return ,checked for blockage, found nothing (except for inside heater, couldn't get to it) no change. Backwashed numerous times, starts out strong and then peeters out again. I thought the laterals looked fine but should I replace them next ? I am at a loss....27 by 52 above ground pool , 1 hp pump, 150ilbs of sand in sand filter.

InyoPools Product Specialist  Posted: 5/24/2017 

Heather - Your pump is probably. I would check for a clogged impeller. See our guide on "How To Clean Out a Pool Pump Impeller". The air in the strainer basket is due to a suction leak between the pump and the skimmer. See our guide on "How to Identify and Correct Air Leaks".

 Posted: 5/22/2017 

Last year (bought the house in August 2016) there were a few bubbles in the pump housing. The service man replaced the O ring gasket. Now that the pool has opened this spring. There are A LOT of bubbles that won't go away. The pressure is about 12 which is normal from last year. I have checked the baskets in the skimmer and pump house. Is it possible the pump is going bad? or there is debris in the impleller?

InyoPools Product Specialist  Posted: 5/15/2017 

B Holland - I'm surprised if you had enough heat to melt the basket, that some of the motor circuits didn't get fried too. But if the motor is still running, you might be ok. Check the shaft seal. If the motor is run without water for a period of time, it melts and starts to leak water over the motor windings. Water would be leaking out the bottom of the motor. That seal should be replaced along with the other pump gaskets. It the diffuser was melted, that would decrease your water pressure. Check that too. Also, check that your motor's impeller is not clogged.

 Posted: 5/14/2017 

We just got our cover off of the pool and went to get everything going. During the winter I shut the pump off because it had no water running through it and the basket was melted inside. The motor still spins, the impellar seems to be fine but even when running on waste or recirculate it barely moves water, it doesnt fill the pump completely but it does move some water. Just curious if my motor, seals or what might be wrong or needing to replace.

InyoPools Product Specialist  Posted: 4/17/2017 

Steve - If you just changed the filter and everything was working before that, I would concentrate on the filter. Check to make sure all connections to the filter are tight. Depending on your filter type, check that the O-ring between the two halves of the filter tank is seated properly and that the halves are screwed together fully.

 Posted: 4/11/2017 

I have a in ground pool I put in a new filter
I have no leaks no visible water I changed everything but
The impeller. I have 2 psi of pressure then I wake up I have
12psi I come back I have 2 psi. It's not the gauge
Either I've changed it 3 times. Should I change the
Impeller or just buy a new pump. Motor sounds normal


InyoPools Product Specialist  Posted: 10/2/2016 

Lance - A permanent split cap motor does not have a start capacitor, only a run capacitor that helps the motor run during operation. It looks like the run capacitor is under the bump on top of this motor. Look at this capacitor and see if it is leaking or bloated out. Also, check to see if the pump impeller is clogged. For motor tests, see our series of guides on troubleshooting a motor.

 Posted: 9/28/2016 

I have a aoSmith B748 permanent split cap 2 hp 230vac motor/pump. The flow is low and the motor is running hot and tripping the internal overload. Its as if the speed is greatly reduced. The capacitor housing is rusted as if its been a dripped on for some time. I have a volt/amp meter and can run some tests. What tests would you run?

InyoPools Product Specialist  Posted: 6/13/2016 

nutforbriggs - Try running your filter with 1 lb less of DE powder. If that doesn't help, your filter fingers may be clogged with oils and chemical that are hard to remove. You may consider replacing some or all of your filter fingers.

 Posted: 6/10/2016 

I have a Hayward Perflex EC65 filter on my inground pool. We had the pool service open up the other day. After running for a few hours I noticed the strainer basket was low on water; water was coming in but not filling the strainer completely. I bumped it and it filled fine. After a few hours, the same thing. Pressure was initially about 20; saw it climbed to about 32. Took the filter apart and cleaned all the fingers; reassembled as per Hayward directions and recoated fingers with DE thru skimmer. Worked fine for several hours but back to the same problem. Pool is CLEAN. Don't hear an air leak anywhere...frustrated. Hate to call the pool guys back cause it's getting really expensive...THOUGHTS??? Thanks!

InyoPools Product Specialist  Posted: 6/2/2016 

bill - It sounds like you have an above ground pool, so you are running out of places to look. A damaged O-ring on the basket cover is a common source of a suction air leak. I would replace that O-ring with a new one. Remember to lubricate it with a silicon or Teflon lubricant.