How To Determine the Cause of Low Water Flow.

WRITTEN BY:  Inyo Pools

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

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.

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.

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.

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.

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.


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Inyopools  Posted: 06/24/2017 11:01 AM  Latest Inyo Product Specialist

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".

john  Posted: 06/22/2017 9:24 AM  Latest

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  Posted: 06/17/2017 11:54 AM  Inyo Product Specialist

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.

Van  Posted: 06/14/2017 7:37 AM 

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  Posted: 06/13/2017 16:24 PM  Inyo Product Specialist

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".

ADK  Posted: 06/12/2017 23:12 PM 

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

Anoula  Posted: 06/12/2017 18:17 PM 

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: 06/12/2017 13:28 PM 

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  Posted: 06/11/2017 22:32 PM  Inyo Product Specialist

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.

Rob1  Posted: 06/09/2017 23:38 PM 

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  Posted: 06/08/2017 23:00 PM  Inyo Product Specialist

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.

Van  Posted: 06/06/2017 12:02 PM 

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  Posted: 05/24/2017 9:33 AM  Inyo Product Specialist

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".

Heather  Posted: 05/22/2017 9:43 AM 

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  Posted: 05/15/2017 14:06 PM  Inyo Product Specialist

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.

B.Holland  Posted: 05/14/2017 18:13 PM 

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  Posted: 04/17/2017 0:05 AM  Inyo Product Specialist

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.

Steve  Posted: 04/11/2017 20:34 PM 

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  Posted: 10/02/2016 12:18 PM  Inyo Product Specialist

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.

Lance  Posted: 09/28/2016 19:54 PM 

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  Posted: 06/13/2016 13:21 PM  Inyo Product Specialist

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.

nutforbriggs  Posted: 06/10/2016 22:08 PM 

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  Posted: 06/02/2016 16:51 PM  Inyo Product Specialist

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.

bill  Posted: 06/01/2016 13:48 PM 

I am having issues with low flow coming out of my pump. I removed the filter from the equation by going straight to the pool from the pump and still have low flow issues. I checked and the impeller is not runs full speed. Hayward said I seem to have an air leak. I have a new hose from the skimmer to the pump and new clamps on both ends of that hose. I am not sure what else the issue could be. Is it possible the basket cover has an air leak in it? Should I replace the o-ring gasket on the basket cover? I'm at a loss.

Inyopools  Posted: 05/30/2016 10:06 AM  Inyo Product Specialist

Charlie - If your filter has a breather tube going up the center of your filter top to bottom, check to make sure it and the screen cap are not clogged. If it is clogged, you may have air building up in the top of the tank causing backpressure.

Charlie  Posted: 05/26/2016 9:07 AM 

I have cleaned my filter spotless. I turned it on everything was great. Then the pressure inside increases and the water flow into the pool decreases. I backwash a few times then everything is good for about a half hour. Is there anything else I could check? Doesn't sound like its sucking air. Pump is running

inyopools  Posted: 10/19/2015 10:37 AM  Inyo Product Specialist

Dwalsh - If your pump has prime and is pumping without significant bubbles showing under the strainer cover, I would guess that you have a blockage somewhere. Check your pump's impeller - "How To Clean Out a Pool Pump Impeller". Then check for blockage in a suction side pipe. If you have diverter valves that allow you to shut off each of your suction side pipes, try turning off each of them to isolate a possible blockage. Most blockages are in the first elbow from the pool. Toys will often get stuck there. You may be able to unblock it using a plumber's snake or you could try blowing it out by removing the pump and attaching a blower to the pipe to blackflush the pipe from the pump to the pool.

Dwalsh  Posted: 10/15/2015 19:14 PM 

Motor went and replaced with exact match. New season started pool and not enough water pressure either with filter or bi pass filter. Checked for air leaks and everything was good.

Inyopools  Posted: 07/28/2014 12:32 PM  Inyo Product Specialist

jack of all - Sounds like you have a suction leak. If you changed the whole filter recently, I would start looking for leaks around those connections.

jack of all  Posted: 07/26/2014 15:29 PM 

have changed the filter (50) in our spa/pool for baptism and have problems with surging flow and pressure. Tried to back flush with garden hose but still have the problem. Can t tell if the pump has anything in it. Also can t tell if there is air leak( most of suction is inaccessible. Starts up ok but after a couple minutes surges starts. Have worry that continued use will damage the pump.

Inyopools  Posted: 04/01/2014 11:30 AM  Inyo Product Specialist

Jordan - You pool water has something suspended in it that's clogging your filter. Take a sample of your water to a pool store and have them check it to make sure your pool's water chemistry is within limits. If your water chemistry is good, give us a call to discuss what might be added to reduce the suspended matter.

Jordan  Posted: 03/31/2014 12:43 PM 

I run my pump without a filter and it flows like a river but whenever I put my filter in, I get low flow and sometimes trickling. I have to pressure wash the filter almost every day just to keep a good flow. I'm certain that my problem is the filter but it is literally 4 months old..

Inyopools  Posted: 06/13/2013 12:38 PM  Inyo Product Specialist

Help!! - First thank you very much for your feedback. It will help us on the next customer's question. For a leaf collector used in line with vacuuming, we would recommend a Clear Leaf Trap 186A for Pool Cleaner.

Help!!  Posted: 06/12/2013 17:09 PM 

Thank you so much for your help! It turns out all it was was a blockage in the skimmer line. Phew! I just kept at it using the priming plug and filling pump with water. I ran it on recirc and eventually it cleared! I then backwashed and rinsed filter.
What do you recommend to use when vaccuming as I seem to have a lot of debris in pool due to lots of trees. I use a skimmer sock when filtering but have nothing for vacuuming so I don't run into this problem again. I have seen leaf collectors for automatic ... anything for regular?
Thanks again!!

Inyopools  Posted: 06/11/2013 11:08 AM  Inyo Product Specialist

Help!! - I'm not sure what's going on here. You are correct. If you run in recirculate mode you shouldn't have to worry about the filter, but? Try a couple of other approaches. Take the plug out and fill the strainer basket with a hose for 3-4 minutes to get some water into all of the pipes. Close the strainer basket. Then try setting the multiport valve to filter and running the pump for 3-4 minutes to see if it will prime.

Help!!  Posted: 06/10/2013 17:17 PM 

I took apart the pump and the impeller is prestine. I do start the pump on high until it primes.
How can I tell if the filter is clogged? My psi is at zero and I prime the pump on recirc.
The purpose of the priming plug is to block skimmer while forxing water through the lines out the jets to rid the lines of air. When I first primed it before I vacuumed, priming plug worked perfectly and did what it was supposed to, stayed in skimmer until I pulled it out. Now the water pressure forces it back out but doesn't go through the lines

Inyopools  Posted: 06/10/2013 13:34 PM  Inyo Product Specialist

Help!! - Sounds like you covered most of the bases. A couple of comments. First the simplest. Is it possible that this 2-speed motor is starting up in low speed. It has to run at high speed initially to prime the pump. Next, since there was a lot of debris in the strainer basket, is it possible that some of the debris got into the pump and clogged the impeller? Then check to see if your filter is clogged with debris.

Help!!  Posted: 06/09/2013 20:42 PM 

We opened our in-ground pool last weekend. We took the cover off, filled it up to the line with water, and put degreaser in, changed out the sand (21" cooper ranger". When we went to turn the pump (jacuzzi magnum force) on, it wouldn't prime. Eventually found out we had a crack in the bottom. So we bought a good condition used 2 year old starite 1hp 2 speed pump from a guy who was closing his pool. Hooked it up, got rid of the leaks, primed it using a priming plug and it worked great!
I tried cleaning the bottom of the pool with the leaf net before I started vacuuming on waste, and got as much as the leaves out as I could. I vacuumed the pool on waste, until the water got below the skimmer (still learning about how to properly vacuum with the water above the skimmer so I don't lose suction. I cleaned out the pump basket which was overflowing with leaves and debris.
I filled the pool back up to the line, but now I can't get it to prime. I blew out the line going from pump to skimmer thinking it was a blockage, I took apart my pump to see if it was the diffuser and it was pristine. When I put the priming plug in, the pressure kicks it back out again. We found we had 2 small leaks in the line from skimmer to pump and repaired those. I try to recirc the filter to prime it but nothing goes to the jets. There isn't enough pressure or water coming through to backwash properly either.
I am at my wits end as this pool has been nothing but problems since we bought the house last August. Shy of paying a fortune to have someone come out, how do I fix this problem I am having, or what could be causing it?