How Do I Correct Low Water Pressure?

How Do I Correct Low Water Pressure?

Correcting Low Water Pressure in Your Pool System

One day you come out to look at your pool and you notice that the water flow isn’t what it used to be. Your pool is cloudy or starting to get a tinge of green; your suction cleaner has stopped; your fountains or bubblers are barely generating columns of water; or you feel less water coming out of the return port. What happened and how do you fix it?

Many people equate low water flow to low system pressure. While it is true that many causes of low water pressure are due to low system pressure, low water flow can also be caused by high pressure. Pressure is typically measured at the pressure gauge on top of the system filter. This blog post will discuss causes of low water flow due to both low and high system pressure.

Causes of Low Water Flow Due to Low System Pressure

If your pressure gauge is showing a low reading and your pool is showing symptoms of low water flow, here are some of the probable causes:

Clogged skimmer basket
If your skimmer basket is full of debris, you are effectively shutting off the pipe between the skimmer and the pump. Generally this will reduce the flow of water to the pump. If less water enters the pump, the pump is moving less water out. This means the pump is doing less work that in turn will reduce water pressure.

Solution: Remove debris from the skimmer basket.

Clogged strainer basket
It is the same story as above. A clogged strainer basket means less water flow that leads to less water pressure out the returns.

Solution: Remove debris from the strainer basket.

Clogged suction pipe
A clogged pipe from the skimmer, suction line or main drain reduces the amount of water to the pump which can reduce water flow to the pump and create low water pressure out the return lines.

Solution: Push a plumber’s line down the skimmer or suction ports to see if you have a clog near the entrance. If there are no clogs there, you can try opening up the line before the pump to blow out the suction line backwards from the pump to the pool.

Clogged impeller
This problem is common, but often overlooked. If the impeller becomes clogged with debris, water can’t rotate out the sides of the impeller. This decreases suction which reduces water flow through the pump.

Solution: Clean out the impeller. See our guide on “How To Clean Out a Pool Pump Impeller“.

Too many features being used
The pump is only designed to move so many gallons per minute (GPM.) Too many water features are like too many hoses on a sprinkler system. The first one has great pressure. Subsequent hoses will reduce the water pressure.

Solution: Alternate which features are turned on or replace the motor in your pump with a larger one. Make sure your existing filter will support the larger pump. You may also have to replace the filter if you increase the pump’s horsepower.

Increased resistance (Head)
If you have just added a suction cleaner to your pool system, it may have increased the resistance to water flow to the pump. The hose adds another 30 or so feet to the piping which adds to total resistance. Also the hose is relatively small, ~1 ¼” diameter and ribbed which adds further to resistance.

Solution: Close off the main drain partially to provide more suction to the suction port.

Causes of Low Water Flow Due to High System Pressure

If your pressure gauge is showing a HIGH reading and your pool is showing symptoms of low water flow, here are some of the probable causes:

Clogged filter
If water can’t get through a clogged filter, you will have less water flowing out of the filter. This will increase system pressure and reduce water flow.  Solution – Clean/backwash the filter.

Solution: Clean/backwash the filter.

Too much sand in the filter
If your sand filter does not have a space of at least 6” between the top of the sand and the top of the filter, you will not be able to clean the sand sufficiently during backwashing and rinsing. The sand must be able to be lifted into this space during backwashing to loosen the debris out of the sand.

Solution: Remove the top layer of the sand to create a 6” space.

Too much DE in the filter
If you put too much DE into your DE filter, the grid will be coated too heavily restricting the flow of water through the grids. Restricted flow will increase system pressure and reduce water flow.

Solution: When you backwash your DE filter, only add back 80% of the DE powder. The filter retains about 20% of the old DE powder during a backwash.

Opposing back pressure
If your system develops an air leak on the suction side of your pump, air can collect in the top of the filter tank during operation. Over time this air will build up back pressure in the tank that will oppose the flow of water into the filter. Gauge pressure will go up and water flow will go down.

Solution: Correct the air leak. See our guide on “How to Identify and Correct Air Leaks“. Also check the air breather tube in your filter to make sure it isn’t clogged.

Too many return valves shut off
Make sure you have enough of your return valves open to balance the flow of water into and out of the system.

Hopefully this blog post provided you with enough information to isolate and correct the problem(s) with your pool’s low water flow. If not, give us a call at 877-372-6038 and one of our service reps should be more than happy to assist you. Have a good pool day!

16 thoughts on “How Do I Correct Low Water Pressure?

  1. Was cleaning the pool and then turned it back to circulate now it’s not reading on the gauge. We thought we needed the suction adapter where you cover it then vacuum and after doing that theres Little suction and bubbles but fine before I cleaned the pool and when cleaning the pool is there a way you can vacuum using the sand filter and it not get in the filter that covers the pool hole.

  2. I just had an inground pool installed. We had so much suction our pool installer said we should not keep it open all the way. It was so much suction that it caused our skimmer basket to get stuck. We had to cut it out and purchase a new basket. Every since that happened, we hardly have any suction with the line 100% open. Any idea on how this can happen? Our pool person doesn’t seem worried about it but it isn’t like it was before and now barely pulling into the skimmer. All the filters have been cleaned.

  3. I have similar issue and think i have isolated it to filter, since pool flow is superb even with lower pump speeds when i go to RECIRC. Through my new DE filter, the skimmers don’t catch any surface debris and you an barely feel circulation at jets.

    I have backwashed it like crazy, even trying without adding DE.

    Filter was put in in may 2018. Pentair FNS plus 36 using cellulose fiber, not DE. Pool is about 14,000g in-ground.

    Is filter undersized or should i take it apart and clean thoroughly this weekend?

    My older sand filter had great flow, just collapsed laterals and blew it’s top….

  4. Hi! I have an above ground pool! We’ve had issues since the start of summer because we had to change the sand and the laterals inside the filter. Now we have low water pressure. Help! I’ve back washed 28822 times. It has strong pressure for about 40 mins then slowly stops. I’ve spent about 400 on chemicals I do not want to start the process over again! Idk what could be causing low pressure. I’ve done everything

      1. I have similar issue and think i have isolated it to filter, since pool flow is superb even with lower pump speeds when i go to RECIRC. Through my new DE filter, the skimmers don’t catch any surface debris and you an barely feel circulation at jets.

        I have backwashed it like crazy, even trying without adding DE.

        Filter was put in in may 2018. Pentair FNS plus 36 using cellulose fiber, not DE. Pool is about 14,000g in-ground.

        Is filter undersized or should i take it apart and clean thoroughly this weekend?

        My older sand filter had great flow, just collapsed laterals and blew it’s top….

        1. Open the filter to complete a deep clean and inspection of the grids and the manifolds. With the filter being relatively brand new, it surprises me that you are experiencing this degree of flow troubles. Considering giving the grids a chemical soak to clear them of any lingering debris.

  5. H Chuck,
    Recently after the last 2 professional pool cleans i notice very low pump pressure and inlet jets are barely pushing the water. Nothing is going into the skimmer box.
    This is only happening AFTER Professional Pool Clean. Before pool clean pump pressure is very good. No issues.
    First time this happened was last month’s clean and i called him to ask about this. He said i need to clean the filter, even though i was billed for equipment check etc. i was going to do it myself after googling how to clean it. This has just happened again where pump pressure is so low and jets hardly rippling the water…
    What is causing this? From great pressure before he ‘cleans’ the pool
    And immediately after basically No pressure.
    He does Not Vacuume ever, brooms the pool and stirs it up and runs it through the filter. Empty the skimmer basket if necessary. Tests water. That’s pretty much it.
    To my mind i doubt the filter is being cleaned after his clean method but being billed for a complete clean. Then for a 2nd filter clean 2 days after the job.
    Hope you can give me some idea about this please.

  6. Replaced the slider valve with the DE Multiport valve, and since I was replacing it I changed the PVC out from the pump from 1.5″ to 2″ since the valve had 2″ connections. In the last several days the pump pressure is only showing 12 PSI or so, after a backwash it goes to 18, but then drops in about an hour or so, water still cloudy but flow seems normal to me, pulled motor and replaced Diffuser O-ring, cleaned impeller. Out of ideas on what to try next. Thought of replacing the impeller, seals, etc. but no leaking but maybe the motor isn’t spinning the impeller fast enough? Is it possible that the DE Multiport valve is leaking or not sealing correctly and letting water flow incorrectly? valve was brand new install at the start of this year.

    1. Hi Chuck. I’m not sure you have a low-pressure problem. Systems normally operate at 10-12 psi I don’t understand why your psi increases to 18 after a backwash. Normally when your system increases 10 psi above your starting psi (12), you backwash your filter to clean it of decontaminates and reduce the psi back to 12. Unless you see a measured decrease in water flow, I’d say your system is operating as it should. If you have a problem with cloudy water, try pulling out your grid assembly and taking it apart to check and thoroughly clean each grid.

      1. Dennis,
        Thanks. When the pool was originally installed the pool company said our pressure should be at 20psi, when it jumps to 30 it is time to backwash. That lasted for years, pool has been in ground for 15+ years, with the slide valve, but I got tired of it sticking and replaced it with the multiport valve at the start of this years pool season. Maybe changing the pipe to 2″ from 1.5″ from the pump output to the filter dropped the pressure due to larger water volume being moved over the same length of time? Having just pulled and cleaned all the filters I know they should be fine. I’m assuming the multiport valve is seal is okay or would it be causing the low pressure signs if it were broken or leaking between segments? Wish you guys had a location in the Pacific Northwest, although Florida is much, warmer… THanks

  7. I have a in ground pool that I noticed the water was beginning to look cloudy and has been crystal clear and beautiful all summer. While vacuuming that evening I notice I seemed to be having a issue with the amount of suction the vacuum had. It just wasn’t as strong as normal. I unhooked the vac and began the backwash and rinse process. After completing that I sit and watched the skimmer….. it didn’t seem to be catching all the little things on the surface of the water. I went to my psi gauge and it was running 7psi. Then I noticed the return on the end of the pool where the skimmer is located has maybe half the pressure it normally does. I have backwashed and rinsed repeatedly 3 times. When I first cut everything back on after rinsing and backwashing, I have strong return pressure but only for a minute….literally a minute. The return on the other end of the pool closest to the filter (sand filter by the way) has normal pressure. I am new to this whole pool thing. This was my dad’s place and I just recently moved here. Unfortunately he is not here for me to ask. My local pool company is so high for ANYTHING AND EVERYTHING THEY ARE CALLED OUT TO DO!!!! I hate for this to be something simple and I call them and pay all of that money when I could have taking care of this myself. Any ideas where to start?

    1. Hi Geri – The first thing I’d check for is a clogged impeller. It is a fairly common problem and would definitely cause low water pressure in your system. See our guide on ” How To Clean Out a Pool Pump Impeller”.

  8. Hi Lori. If you have a typical above ground pool, you don’t have that many things to look. at.
    About all that’s left is the filter. If your multiport valve has a recirculate mode that bypasses the filter. set it to recirculate and see that that improves your water flow. If it does, you may have to change your sand, especially if that hasn’t been done for 5 years. Also, check the hose from between the pump and the filter. Disconnect the hose at the filter side. Turn the pump on. If you don’t have good flow, you may have a block in that hose.

  9. Help! I have the exact same problem that you described above but I’ve done everything on the list and my pool us no better, I’ve even replaced my pump/motor because I thought maybe it was getting weak, I’ve had a pool for about 5 years now and have never had this problem. My pool is a 22 by 52 above ground pool with a sand filter system. Do you have any advice?

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