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 130)

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User: Inyopools

Clueless - Not sure what you are referring to when you say "valves". If they are diverter valves that are used to turn off/on parts of the pool, I would say to leave them open while the multiport valve is in backwash mode.

User: Clueless

Sorry of this sounds stupid, but I really don't know what I am doing. This information is great, but I can't get my head around when to open and close the valves to the pool? Should I have both valves open before I star this process and leave them open throughout?


User: Inyopools

Justin J - If you have to backwash that frequently, you are probably way past the time to replace the filter's sand. I would do that first. See our guides on "How To Change Sand In a Sand Filter" or "How To Replace the Sand in a Pentair Triton 2 Side Valve Sand Filter" for further instructions. Then check the spider gasket in your filter Multiport Valve (MPV) to see if it is damaged and is possibly leaking between ports. See our guide on "How to Replace a Spider Gasket on a Multiport Valve".

User: Justin J

I have a couple questions. Why wont my filter backwash unless I run the rinse cycle first. If I go from filter to backwash and turn it back on nothing happens, but if I go from filter, to rinse, and then to backwash its backwashes just fine. Also it seems I have to backwash frequently, like every couple days. THe jets in the pool get weak, suction is weak and the psi is up. SO i backwash and I'm good for another couple days. IS it time to replace the sand and/or filter completely? I recently bought this house so I have no idea how old the equipment is.

User: Mindychua

Im trying to open the pool for the year, and the filter is cycling through power. It'll run normally for a few seconds, then have a burst of power for a few, then back and forth? I tried back washing, but I was worried something was really wrong, so I turned it off. The pool is an absolute mess, and I'm not sure if that has something to do with it. Thanks! I have a video of it would help.

User: Inyopools

Dawn - I also don't understand why your pool continues to fill with water. Your pool is a self-contained system. The extra water has to come from somewhere outside the system like rain or runoff into the pool. Do you have a sprinkler system that is spraying water into the pool?

User: Dawn

My pool continues to fill with water. When I backwash it is barely backwashing. Then when I rinse the gauge rises back up. Pool is now cloudy but mostly concerned why the water level continues to rise.

User: Inyopools

Michelle - You only have to backwash a sand filter when the sand is clogged with decontaminates. You will know this when the pressure gauge on your filter creeps up to 10-15 psi above its normal operational range and your spa starts to look cloudy. With little use, I would doubt that you would need to backwash more than 1 or 2 times a month. Depends on how much outside debris is getting into your spa.

User: Michelle

HI There: We have a spa with a sandfilter at work. Is it necesary to backwash the pool on a weekly basis if no one has been in the spa during that period?

User: Inyopools

BT - See our guide on "How To Go From Cloudy To A Crystal Clear Pool". Also you might want to try a clarifier. This one has good reviews: "Concentrated Clarifier 1 Qt". The sand “puddles” may fine sand getting through the filter, a damaged spider gasket or a broken lateral.

User: BT

Have a new Hayward sand filter and pump. After back washing and rinsing (turning the pump off in between each step), the water going back into the pool doesn't look clean. The pool is clear but has a very slight cloudiness to it. I've shocked and kept up with chlorine tabs in the skimmer, and have vacuumed (there are a few small "puddles" of what looks like sand on the bottom after every few days). Any thoughts?

User: Inyopools

green pool - I would guess the water coming out of the waste port just looks clear because you're not seeing a large volume of it. Try collecting it in a large white bucket to see if it has a green tinge to it. See our guide on "How to Clean a Green Swimming Pool (Algae)" for detailed instructions on clearing your algae. Make sure your chemicals are balanced before you shock and put algaecide in. And you may have to do this process a couple of times.


My pool is green and after treating with algacide, the water coming out in backwash mode is clear. What could the problem be.

User: Inyopools

Relabstract - Sounds like a damaged gasket. Check your spider gasket on your multiport valve. See our guide on "How to Replace a Spider Gasket on a Multiport Valve" for more information. Remember to shut off the pump every time you change the valve setting to prevent damaging the gasket.

User: Inyopools

Fuz - Because your pool equipment is above your pool's surface, the water in you pump and filter will tend to drop back into the pool through the suction lines. If your pool equipment is higher than normal, more water will flow back into the pool. You might consider putting in a check valve between the pump and pool to stop this back flow when you shut the pump is off. The initial bubbles coming out of the returns during priming is natural. My guess on the dirty water is it's coming from the filter. Sounds like your filter is draining too when you shut the pump off and when you turn it back on and refill the filter, the action may be dislodging some of the dirt in the filter - somewhat like a partial backwash only the dirt is going out the return ports rather than the waste line.

User: Relabstract

When I set back to Filter (after Backwash & Rinse), blows sand back in Pool??

User: Fuz

Hi inyopools, I have a sand filter (not sure what make but is has a plastic casing on top so you can see the water going through. The water seems clear to me but when I turn off the pump, the water seems to drain out over about 5 minutes. Then if I restart it after about an hour or more, it takes about 90 seconds to find its prime, and when it does a lot brown water come out of the return jets followed by some large air bubbles for a minute or so? Any ideas what is wrong as besides this the pool seems fine but I'm having to run the pump 24/7.

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?

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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.