How to Correct Low Water Pressure in Your Pool System

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Low pressure is a pool term that is often used to describe weak jets as well as a low PSI reading on the filter’s pressure gauge. High PSI readings will also cause low water pressure. A low or high PSI reading is anything outside the normal operating pressure of the filter. Weak jets, air bubbles, slow pool cleaners and weak water features are obvious signs of low pressure. This guide addresses the common causes of low water pressure in a pool.

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Step 1

First, a short discussion on how a pool system works. The piping in a pool has two sides: the suction side that is before the pump and a pressure side that is after the pump. The pump creates a vacuum that sucks water from the pool and then pushes it back into the pool through a filter. A leak in the suction side will cause air to be sucked into the system. A leak on the pressure side will cause water to spray. If you have a blockage in the suction side of the pump, the blockage will restrict the amount of water to the pump that will result in low pressure. A blockage in the pressure side, like a dirty filter, will have the opposite effect and will cause the pressure to go up. Here are the common causes for low pressure - the easiest to fix is explained first.

Step 2

LOW WATER LEVEL (Low PSI) - The water level should be at least halfway up the skimmer door's opening. If it's too low, the pump will have trouble priming and the water pressure will drop.

Step 3

CLOGGED SKIMMER BASKET (Low PSI) - 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 the pump has less water entering it, it is moving less water out. This means the pump is doing less work that in turn will reduce water pressure.

Solution: Clean your skimmer basket by removing any debris.

Step 4

CLOGGED STRAINER BASKET (Low PSI) - 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: Clean your strainer basket by removing any debris.

Step 5

CLOGGED FILTER (High PSI) - Again, if water can't get through a clogged filter, you will have less water flowing out of the filter. Incidentally, this will increase the water pressure in the filter signaling that it is time to clean the filter.  

Solution: Wash your cartridge filter. Periodically soak the filter overnight in a TSP solution to get the grease and gunk out of the folds. Grease is produced by suntan lotion, sebum (oils secreted by the human body) and pine tree needles. Then soak the cartridge in a weak solution of muriatic acid (10:1) to get the minerals out of the folds. Use the TSP before the acid or the gunk will set up in the folds. For sand filters you will need to backwash as required. Change the sand every five to seven years. In between changes, if sand has caked on top, take one to two inches off at the top and replace it with new sand.

Step 6

CLOGGED IMPELLER (Low PSI) - This problem is 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".

Step 7

SUCTION LEAK AT PUMP (Low PSI) - The pump lid o-ring, pump intake fitting, and drain plugs are common areas to draw in air. A suction leak in the suction side of the pump can cause a number of problems. If it's large enough, too much air will be sucked into the system, and the pump will lose prime. If it's smaller, air will be sucked in through the pump and start to collect at the top of the filter tank. After some time (sometimes a few hours) air pressure at the top of the tank will create enough back pressure to reduce the flow of water significantly. When the pump is shut off, this back pressure will cause the water in the suction pipe to surge back and sometimes create a column of water up though the skimmer.  

Solution: Find the suction leak and close it. See our guide on "How to Identify and Correct Air Leaks".

Step 8

SUCTION LEAK AT DIVERTER VALVE (Low PSI) - The diverter valves in front of the pump control the flow of water from the skimmer, main drain, and vac lines. They also have seals in them that can go bad and allow air to enter the system. Again, air will cause the water pressure to drop and will lead to the pump losing prime.

Step 9

SUCTION LEAK AT PLUMBING FITTINGS (Low PSI) - Any fitting on the suction side of the system can draw air. Cut out and replace any fittings that have an air leak.

Step 10

CLOGGED PIPE GOING TO THE PUMP (Low PSI) - 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 stiff wire down the skimmer or suction ports to see if you have a clog near the entrance. If there are no clogs there, you may have to get a pool professional to come in to check your pool pipes.

Step 11

TOO MANY FEATURES OPENED - The pump is only designed to move so many 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 it.

Step 12

PUMP IS TOO SMALL - If your pump's size was calculated for you initial pool system and you have added more equipment onto that system, you may have exceeded the pump's capability to supply the GPM that is now required. Also, if you have moved your pump significantly further away from the pool, which required more pipe, you may have increased water resistance in the pipes that exceeds the pump's capability.   

Solution: Replace the motor in your pump. Note you may also have to increase the size of your filter if it won't handle the increased GPM water flow. See our guide on "How To Replace the Motor on Your Pool Pump".

Step 13

BAD PRESSURE GAUGE - Pressure gauges on top of the filter do go bad. Your apparent low-pressure reading may be due to a faulty gauge.

 Solution: Replace the pressure gauge. See our guide on "How To Replace a Pool Filter Pressure Gauge on a Cartridge Filter".

Comments

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(1 to 40 of 314)

 Posted: 6/28/2019 

Thank you, I am a 65 year old female from Wyoming. My pool company Watco at Billings went under last year it's really hard to get help here!
 Reply

 Posted: 5/29/2019 

I have a Clearwater II cartridge system. Low inlet and out let pressure. Above normal pressure in cartridge tank. Cartridge less than 1 week old. Used plumbing snake on suction and outlet side. No obstruction. Any suggestions
 Reply

InyoPools Product Specialist  Posted: 5/30/2019 

Are you sure you purchased the correct cartridge size? Some models have cartridges with the same overall dimensions but different square footage and flow ratings. If you bought a smaller cartridge, the flow would be restricted as you explained.
 Reply

 Posted: 5/23/2019 

I have a DE filter, cleaned it a few times. If I put it on recirculating or backwash I have plenty of pressure. Run it on filter starts strong and pressure does out in a few minutes.
 Reply

InyoPools Product Specialist  Posted: 5/24/2019 

Give your grids a chemical soak to clean out the nooks and crannies of the material. Even though the DE powder does most of the filtering, the grid material can get caked with dirt and muck too.
 Reply

 Posted: 5/22/2019 

Looking for advice on low flow only when on filter. Flow is great on drain and backwash, but low on filter (even the clear vessel barely fills up one third). I have backwashed for several minutes still without luck. Obviously the pump is working given the strong flow on drain. Would I have a blockage out back towards the pool?...need to replace the sand? How can I test and eliminate? Thanks in advance.
 Reply

InyoPools Product Specialist  Posted: 5/23/2019 

How old is the sand?
 Reply

 Posted: 5/23/2019 

Found out this morning that the sand hasn't been replaced - approx 8 years old. Live in Canada so only getting 3 months use (at the most) and from what I understand from previous owner, have never had any issues last summer. I guess I should first check the filter handle mechanism for damage and then replace the sand?
 Reply

InyoPools Product Specialist  Posted: 5/23/2019 

It seems like the valve is working correctly. If you backwash and there is no change in the flow in filter mode, it's time to change the sand.
 Reply

 Posted: 5/18/2019 

I had a Jandy Stealth pump that was just replaced early fall last year, and given a Jandy VS FloPro. It now warmer out and algae growing. Variable speed pump is not making the rest of the unground cleaning heads pop up. Do you think the pump has anything to do with the pool not getting clean? Every few days I have to shock the pool.
 Reply

InyoPools Product Specialist  Posted: 5/20/2019 

Have you increased the run speed and time of the pump? The variable schedule may be set at a run time that is ok for the cooler months but not suited for the algae bloom season.
 Reply

 Posted: 5/17/2019 

The water flow in my pool goes low after a few hours. To resolve it I backwash, and the flow is fast & efficnet. But then again after a few hours there is barely any flow.
 Reply

InyoPools Product Specialist  Posted: 5/20/2019 

Is your pool green or cloudy? If this is a sand filter when was the last time you changed the sand?
 Reply

 Posted: 5/20/2019 

The water is blue and clear. The pump ocassionally times out because of a priming error (not enough water filling into the strainer pot). The skimmer basket is free of debris, the strainer basket is also free of debris, the impeller seems to work fine, water flows out of the returns. The filter is a DE filter. It has a reading of about 18 psi. Also, the backwash flow is normal. I’ve released air from the knob at the top of the DE filter. The restricted water intake from the main skimmer line results in the Inteliflo chlorinater reading a no flow error. The skimmer basket initially has good flow after a backwash but then return soon to having low flow and priming error.
 Reply

InyoPools Product Specialist  Posted: 5/20/2019 

After the flow begins to fall off, and you backwash the filter, do you have to manual prime the pump or can it prime itself? Also when priming, do you have to release air out of the DE filter?
 Reply

 Posted: 5/20/2019 

Sometimes it can prime itself, other times it can’t. It doesn’t consistently do one or the other. After a little while, it consistently stops having that good flow where debris is seamlessly drifting into the skimmer. I release the air after backwashing but that doesn’t seem to make a difference.
 Reply

InyoPools Product Specialist  Posted: 5/21/2019 

Give this guide a read; it may help you find the problem: How to Identify and Correct Air Leaks
 Reply

 Posted: 5/16/2019 

I have a Hayward DE 60 sq ft filter. I just backflushed it for the first time yesterday. After backflushing the pump water flow rate is much lower for some reason. Any ideas?
 Reply

InyoPools Product Specialist  Posted: 5/16/2019 

Did you bleed the air out of the system using the air relief valve on the filter? That filter only requires 7.5 pounds of DE. Too much DE could cause a decrease in flow. Also, look for any air leaks on the suction side of the system.
 Reply

 Posted: 5/16/2019 

What would cause water pressure to come from my Polaris hook up when the booster pump is off but the pool filter is running. Is my dverter valve bad?
 Reply

InyoPools Product Specialist  Posted: 5/16/2019 

Hello Shannon - It is normal for a small amount of water to push through the Polaris even though the booster pump is not running. The line to the Polaris doesn't automatically close when the booster pump is off.
 Reply

 Posted: 5/16/2019 

Hi - just opened pool and getting green water clear again. In the process of course there are many backwash cycles when the pressure rises. This year something different is happening with my (sand) filter. It holds a steady pressure of 20 as usual. The pressure never rose after hours of running - instead it eventually went down to 18. I then backwash and it goes back to 20 unit it I guess is dirty after some time and drops to 18. The reverse is happening from what is normal and what always happened in prior years. Why would it go down when dirty ?
 Reply

InyoPools Product Specialist  Posted: 5/16/2019 

Hello Paul - It's possible that the pressure gauge is bad. It's also possible to have a small air leak that slowly reduces the pressure in the system.
 Reply

 Posted: 5/11/2019 

My pump will backwash and rinse but won’t circulate water to pool and back thru pump!!
 Reply

InyoPools Product Specialist  Posted: 5/13/2019 

Is this a sand filter? If so, how old is the sand?
 Reply

 Posted: 4/27/2019 

I just installed new sand filter and pump. Pump runs, but I have no pressure reading at all on the gauge. It is zero. There is water coming out the return hose, but zero on the gauge.
 Reply

InyoPools Product Specialist  Posted: 4/29/2019 

The pressure gauge may be broken; they can be fragile. Contact the company from who you purchased the filter to get a replacement, or pick one up at a local hardware store.
 Reply

 Posted: 4/24/2019 

Have trouble with suction in my skimmer, jets still work but no water suction in skimmer. Check for any clog there is none. What could be causing this? Went through all your steps and nothing’s working. Please help.
 Reply

InyoPools Product Specialist  Posted: 4/24/2019 

Hello Nikki - If the jets are working normally and the skimmer is not working, my guess is that a valve has closed the skimmer line. It must be pulling all the water from the main drain. Try opening up the valve that controls the skimmer. You may need to close the main drain slightly in order to increase the suction to the skimmer.
 Reply

 Posted: 4/17/2019 

My pool guy just replaced the sand in my filter. Now the water pressure coming back in to the pool is real low. Also I noticed that the clamp ring that holds the head to the sand tank is now split on one side and I hear bubbles in the filter. would those have something to do with the low pressure? Thanks
 Reply

InyoPools Product Specialist  Posted: 4/17/2019 

Hello Bob - We'd be glad to assist you. Do you see air bubbles inside of the pump lid? Are bubbles coming back through the return jets? What is the PSI reading on the filter gauge (if you have one)?
 Reply

 Posted: 4/15/2019 

Went through all the steps above, none of those were the problem. My lovely wife bought a skimmer filter that was too small. Replaced it with the right one and immediately water flow returned.
 Reply

 Posted: 3/31/2019 

My pump works fine for 5 to 10 minutes, PSI gauge is at 18, then the return flow to the pool gets greatly reduced, the PSI gauge stays the same of might occasionally go up to 20. What do you think is wrong?
 Reply

InyoPools Product Specialist  Posted: 4/1/2019 

Have you completed any of the troubleshooting or checked points of concern mentioned in the article?
 Reply

 Posted: 3/15/2019 

Hi thanks to your guide I have sorted out zero pressure problem, this was due to junk that had built up in the pipe just before the pump cage as the mesh holes in filter cage too small to allow the larger bits of rubbish in, I removed the cage basket and pulled a big wad of junk from the pipe! Thanks a bunch as you saved me the cost of a pool repair call out.
 Reply

InyoPools Product Specialist  Posted: 3/15/2019 

Thank you for the feedback, Colin!
 Reply

 Posted: 10/13/2018 

Hi inyo, I've just installed a Davey Powermaster eco 3 speed pump. It's working beautifully. On high and mid speeds the pressure reads normal, but drops to 0 for eco mode. There's still a reasonable stream coming from the jets, and no air building up in the strainer housing. Should I be concerned about this, or will this just be normal for eco mode? Thanks again for all your help!
 Reply

InyoPools Product Specialist  Posted: 10/17/2018 

Hello Graham - It is normal to see 0 PSI when the pump is running on it's lowest speed. Your system is ok if you see movement through the filter, pump, and return jets. Heaters and salt systems likely won't work on that eco mode since those items require a certain flow rate that you probably aren't producing.
 Reply

 Posted: 9/25/2018 

Hello Maxxwell - The pressure usually rises that quickly because the pool is cloudy or the filters need to be soaked in a filter cleaner or replaced.
 Reply

 Posted: 9/24/2018 

Hello, any advice on how to diagnose the PSI pressure to rise to 25PSI only after 5 hours of cleaning the filters? I cannot figure it out. thank you in advance
 Reply