How To Backwash a Pool Sand Filter

Written by:  Danny Rhodehamel

After a period of time, the contaminates in a sand filter start to clog the sand to the point where water flow is significantly diminished and the pressure gauge rises 8 to 10 psi above normal operation readings. To clean out the contaminates, you have to backwash the sand. This guide shows you the steps in backwashing a filter.

Tips & Warnings


Step by Step

Step 1

To prevent damage to the plumbing or valve you must first TURN OFF THE POOL PUMP before moving the multiport valve handle. For maximum safety turn off the power at the circuit breaker to the pump.

Step 2

Your pool filter valve is probably at the FILTER setting for normal operation. Depress the multiport valve handle and move it to the BACKWASH setting. To prevent damage to the multiport valve seal, always depress the handle fully before turning.

Step 3

Make sure your WASTE hose is laid out to where you want to dump the waste water.

Step 4

Turn the power back on and run the pool pump for at least 2 minutes. The water in the sight glass on the side of the valve will change from cloudy to clear.

Step 5

Turn the power back OFF.

Step 6

Depress the multiport valve handle and turn it to the RINSE setting. After backwashing, the sand is loose and needs to be reset. Also any dirty water from backwashing has to be rinsed out of the filter to WASTE to prevent it from returning to the pool.

Step 7

Turn the pump back ON and run filter at the RINSE setting for 1 to 2 minutes.

Step 8

Turn the Pump OFF. Depress the multiport valve handle and turn it to the FILTER setting.

Step 9

Turn the pool pump ON for normal filter operation. Check your pressure gauge to ensure that the pressure has dropped 8 - 10 psi from where it was before backwashing the pool filter.

Comments (1 to 40 of 113)

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User: Inyopools

Ulysses - If you have low flow in all valve settings, it sounds like you have a blockage somewhere in your system. You already checked the pump impeller so that should be good. If you haven't changed your filter sand in 5-7 years, I would do that. Replace the top 6" of sand first to see if that makes a difference. Make sure some of your diverter valves are open - suction side and return side. Try snaking a line through your pipes to see if you have a line blockage. Please send me another comment, when you resolve this issue for feedback. Thanks

User: Ulysses

I do not know what the problem is: My pool pump has been working perfectly for the last couple of years. now, it has no suction to vacuum the pool. When i backwash, it spurs the water instead of what it usually did, water pumping steadily. the same occurs when i rinse.
i've already took the pump apart and found no debris around the propeller. the filters are clean. I do not know what to do

User: Inyopools

Bret - You may have a blown spider gasket in your multiport valve. See our guide on "How to Replace a Spider Gasket on a Multiport Valve" to see how to inspect and replace a spider gasket if required.

User: Bret

Have a Hayward sand filter that is only 3 years old on an in-ground pool. When I shut off the pump, water blows out the waste line and I lose prime in the pump rapidly. It doesn't seem to do this on recirculate, only on filter setting. When I test it on recirculate, I do see some small air bubbles slowly coming up in the pump strainer area. It's a Jacuzzi pump and the o-ring and cap look fine. Any suggestions?

User: Inyopools

clogged line - Sounds like you have a blockage somewhere. Your skimmer line may be blocked again or you may have a blocked impeller. See our guides on "How To Determine the Cause of Low Water Flow" and "How To Clean Out a Pool Pump Impeller" for further information.

User: Inyopools

concerned - If you don't see water going out your waste line while in Filter setting, you are probably OK. To check for sure, see our guide on "How to Replace a Spider Gasket on a Multiport Valve".


I have one skimmer and that is where I vacuum from. I can close the main drain and the skimmer lines. Other than that I can't tell you if I have another line.
Someone did "unclog" my skimmer line but the debris still doesn't pull into the skimmer. Last year anything floating in the poll, thermometer, noodles..... would end up in the skimmer. Now they do not.
I do am new to in ground pool ownership and not a mechanically inclined female.

User: concerned

My house sitter backwash my pool with switching
Switching off the power before changing from
Filter to backwash i know that this is a big no
No i am concerned that ma pool will be damaged how can i establish that all is still well

User: Inyopools

nvr218 - Could just be air mixing with the outgoing water. See if there is a leak in the spy glass O-ring. Capture the water going out of the waste line and let it settle. If it is clear, the milking color is just air.

User: nvr2l8

curious why my backwash is always milky white...regardless of how long i run it. my pool is crystal clear. same thing happened last year too..HELP ANYONE!!!

User: Inyopools

Rookie - It sounds like you are getting air into the suction side of your pump - between the pump and the pool. Try brushing a soapy solution around all your connections between the pump and the pool and see if you can detect bubbles being sucked into a leak.

User: Rookie

I'm a newbie opening our Inground pool. I'm having trouble getting the hayward self priming pump to prime, it gets close but must be air in the line and loses it again. Of course the cell won't chlorinate as it's not getting flow. The sand filter psi is 23 but when I put it in backwash - nothing happens,nothing flows out. Only have one line coming into the pump from the pool so I cannot isolate the skimmer line. Any ideas what my issue is?

User: Inyopools

Vivienne - If you also have little or no flow in "Filter" mode, you may have a badly clogged filter. This could happen if you tried to filter you pool with significant debris in it. Try replacing the top 6" of your filter sand with new sand. If you haven't replaced your sand in 5-7 years, you should replace it now.

User: Inyopools

b52 - Assuming you have a separate suction port for your cleaner, it sounds like you have a blockage in your skimmer line. If you shut off the main drain and the suction port, do you have any flow coming to the pump from the skimmer line?

User: Vivienne

There is no water flow when pump is in backwash mode but flows fine when in waste mode? What could be our problem? We did not have a cover and this is our second year with the pool.

User: b52

My pool man just replaced my DE filter with a Hayward sand filter. Now my skimmer doesn't have enough suction when I have both the main drain and skimmer valves open (normal operation). It suctions enough for vacuuming when I have the main drain closed 3/4. Thus during normal operation the debris floating in pool doesn't get pulled into the skimmer. The pool man refuses to comeback and said he refunded my money. Everything worked at closing last season.

User: Mickie

I am look to purchase the hard hose that goes fron the pump to the sand filter. I have a Hayward pro series pump and sand filter.

User: Inyopools

Rho57 - If you had a lot of debris in your pool that went into the filter, you may have to backwash your pool 2 or 3 times to clear that debris. If you don't have a relief valve on the top of your filter, you can open the drain at the bottom slightly to relieve the pressure. Lastly, you may have a bad pressure gauge that needs to be replaced.

User: Rho57

Our psi is running 25-30 after I backwashed and rinsed. The same as it was before. I have a hayward sand filter and read somewhere that I might need to release pressure but can not find a pressure relief valve at the top of my filter like it said on the web page.

User: Inyopools

McKnight - Most filters operate in the 10-20 psi range so yours is acceptable. When yours gets to 25-30 psi, I would backwash it. If you pump is several feet above the pool level, it will drain back more quickly into the pool when the pump is shut off. Some people put a check valve between the pump and pool to stop the backflow.

User: McKnight

My pressure gauge is staying around 15-20 psi during/after running the pump for 48 hours. Is this a safe "normal" reading? Also, my pump keeps losing prime after just turning the pump off for a very short time to change from filter to another setting (ex: backwash, waste, etc). We just changed the sand this year (first year we have owned the pool, as we just bought the home in December), and found the lateral assembly and center pipe was broken. So of course that was replaced too! What are some reasons the pump keeps losing prime? Thank you for your help! I love this site... it is so helpful!!!

User: Inyopools

Julia - Check to see if you are losing water through the "Waste' port while you are in "Filter" mode. If so, your spider gasket in your Multiport Valve may be damaged and would have to be replaced. Otherwise, if you see no other leaks around your pool equipment, the water loss may be just due to evaporation.

User: PHIL

I have a DE filter with a separation tank. How do I find out which pipe I can use for the waste flow so I can vacuum the pool without clogging up the filter and the bag in the separation tank?

User: Julia

I has to backwash my in ground pool because the level became too high after heavy rain. When finished I turned off pump and turned valve to filter. Now my pool is losing water quite fast.
Did I do something wrong?

User: Inyopools

nodt22 - Sounds like the VS pump is producing more pressure than your system can handle. Most VS motors have a max speed setting that prevents the motor from generating more pressure than your system can handle.

User: nodlt22

i have a sand filter with a vs pump now i have tried backwashing the filter but the pressure makes the backwash hose blow up i could try low speed but the pump has a delay for low speed. can anyone help

User: Inyopools

NDHANSON - I would set the VS Pump at near full speed to increase pressure. It will help raise and then set the sand better.


I have a Hayward sand filter and a Hayward variable speed pump. What is the best rpm to set the pump at for backflushing?

User: Inyopools

Aroddey – 50 is way too high for a psi reading. You typically have to clean your filter at 20-30. If you have very dirty water as you indicate, you may have to backwash your filter repeatedly until it is clear. If you still have a lot of debris in your pool, you should get most of it out thru the waste line and not run it through your filter. If your pool is clear and your gauge still reads high, you might have a bad gauge.

User: Inyopools

Gin – You may have a tear in your Multiport Valve Spider Gasket. See our guide on “How to Replace a Spider Gasket on a Multiport Valve” for more information.

User: aroddey

My pool's psi is at 50. I don't know if this is normal... but I have already backwashed..(really green nasty water..) then I rinsed.. but the psi is still at 50. what do I need to do?

User: Gin

I have no pressure to backwash pressure is perfect till I try backwash what could my problem be and how do I fix it?

User: Inyopools

Barb - You vacuum line may be sucking air. If you are not losing prime in your pump, you may be building up an air pocket in your filter. Check for air leaks in your vacuum hose by holding the entire length under water while the vacuum in on. If you maintain pressure, you have a leak in your hose. Check the hose connections first then take out sections of hose one at a time.

User: Barb

Just wondering why my pressure gauge rises when trying to vacuum my pool then after 5mins there is no pressure

User: Inyopools

George - Not sure what your end result is. After 2-3 days, is the sand gone? Does this happen every time you backwash/rinse? If you recently changed you sand, you may have fine sand in the new sand that gets through the filter. Try vacuuming the sand to the waste port. Also check the spider gasket in your multiport valve to see if it's damaged and is leaking water into the wrong ports.

User: George

Can anyone please assist me.
Sand blowing back into my pool.
After vacuuming, i backwash, rinse and then when i switch the pump on again, sand blows back in the pool.... (this is a new thing)
ive also noticed when i vacuum the sand up, it already starts blowing back into the pool.. after 2 or 3 days the water is crystal clear again... but irritating...
Thank you
George Cape Town

User: Spider

Have a wuring noise at the top of the sand filter coming from the Multport valve handle.

User: Inyopools

Sonia - It sounds like your pump is not priming. If you do not see water flowing in the pump strainer basket, your pump is not sucking water from the pool. See our guide on "How To Prime a Pool Pump" for further instructions.

User: Sonia

Hi, my inground pool has not been use for 2yrs. Now just cleaned & refilled water. Then I started the backwash, but I see nothing happen but the pump is making sound. It's 5 yrs old sand filter. What should I do? Thanks!

User: Inyopools

Lee - Check the spider gasket on your multiport valve to make sure it wasn't damaged. See our guide on "How to Replace a Spider Gasket on a Multiport Valve". Make sure you turn off the pump every time you change the valve setting or you can blow the spider gasket. Also after you backwash, go to a rinse cycle before switching to "Filter" to rinse out any dirt still in the sand after backwashing.

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Tips & Warnings

Don't backwash excessively. Contaminates in the sand actually help the filter work more effectively - to a point. Monitor your pressure gauge for an 8-10 psi rise.

Never move the valve handle when the pump is on.

Don't vacuum your pool in backwash mode. You may clog the collection pipes (laterals) at the bottom of the filter.

Please Note:

Inyo Pool Products is not responsible for any injury or damaged equipment
while using our guides. Using our guides is doing so at your own risk.
These guides are suggested use of your pool or spa equipment and may vary
depending on which product you are using.