What Does Recirculate Do on a Pool Filter? - When to Use It

What the Recirculate Setting Actually Does

On a multiport valve, water takes a different path depending on which position the valve handle is set to. On the FILTER setting, water flows: inlet port to through the filter media (sand or DE) to out the return port to back to pool.

On RECIRCULATE, the valve routes water differently: inlet port to directly out the return port, bypassing the filter media entirely.

The pump is running and water is moving through the pool, but no filtration is happening. Think of it as the pump circulating pool water in a loop with the filter media cut out of the circuit. Inside the multiport valve, a rotary diverter sits on top of the rubber spider gasket. Each valve position lines that diverter up with a different set of ports, which is how one handle controls so many flow paths. On RECIRCULATE the diverter opens a channel straight from the pump-inlet port to the return port, while the channel leading down into the filter tank stays closed.

The practical takeaway: RECIRCULATE keeps water moving so chemicals mix and the surface stays from going stagnant, but the water comes back exactly as dirty as it left. Use it when the filter must be offline or bypassed, not as a way to clean the pool.

Multiport Valve Settings - All Positions Explained

Most sand and DE filters use a multiport valve with six or seven labeled positions. Here is what each one does and when to reach for it.

Note that WASTE is sometimes labeled DRAIN, and not every valve includes a WINTER position. The CLOSED and WINTER positions should never be used while the pump is running, because dead-heading the pump against a closed valve builds dangerous pressure.

When Recirculate Is Actually Useful

During filter media replacement: When you have drained and emptied the filter tank for a sand change or DE grid cleaning, you cannot run on FILTER, there is no media to filter through. Run on RECIRCULATE if you need to circulate shock or algaecide through the pool while the filter is being serviced. The same applies if the media is missing or has channeled badly and you are waiting on a replacement.

Distributing chemicals quickly: If you need to rapidly distribute a shock treatment, clarifier, or liquid chlorine throughout the pool volume, RECIRCULATE lets you run the pump at full flow without any pressure restriction from the filter media. This is useful when the filter is heavily loaded and running on FILTER mode would create high back-pressure. Pour liquid chlorine slowly in front of a return jet with the valve on RECIRCULATE and it spreads through the water in minutes instead of sitting in one corner.

Circulating flocculant before vacuuming to waste: Flocculant works differently from a clarifier. Instead of helping the filter trap fine particles, it clumps suspended dirt and dead algae together so they sink to the floor. The usual routine is to add the flocculant with the valve on RECIRCULATE so the product disperses evenly through the whole pool, then shut the pump off for several hours to a day so the clumps settle. Once everything has dropped to the bottom you switch to WASTE and slowly vacuum the sediment straight out the waste line so it never touches the filter. RECIRCULATE is what gets the product mixed in without immediately pulling it into the media. A pool flocculant or clarifier is the product you would dose during this step.

Troubleshooting filter problems: If you suspect a filter blockage and want to test the pump at low pressure before attempting a backwash, briefly running on RECIRCULATE confirms the pump is working normally. Because RECIRCULATE skips the filter, it is a quick way to separate a pump problem from a filter problem. If flow is strong on RECIRCULATE but weak on FILTER, the filter or media is the culprit. If flow is weak on both, look at the pump, the basket, or a suction-side air leak. Our guide on why a pool filter is not working walks through this diagnosis in more detail.

When NOT to Use Recirculate

As a substitute for normal filtration: Running on recirculate for extended periods means your pool water is not being filtered. Debris accumulates, algae can establish, and chemistry becomes harder to control. The filter exists for a reason, use it. RECIRCULATE is a temporary mode measured in hours, not days.

During algae treatment: When treating algae, you need the filter running on FILTER mode to capture the dead algae cells the treatment kills. Running on recirculate circulates the chemicals but does not remove the dead algae from the water. The filter should run 24 hours per day during algae treatment.

After a backwash: The correct sequence after backwashing is always BACKWASH to RINSE to FILTER. Never skip to RECIRCULATE after a backwash, it does not settle the sand bed and you risk fine media particles returning to the pool. For the full step order, see our how to backwash a sand filter walkthrough.

The WASTE Setting - How Recirculate Differs

WASTE is frequently confused with RECIRCULATE because neither one filters the water. The difference is where the water ends up.

• RECIRCULATE: Water goes pool to pump to back to the pool. No filtration, and the pool water level stays the same.
• WASTE: Water goes pool to pump to out the backwash line. No filtration, and the pool water level drops because that water leaves for good.

Use WASTE when vacuuming algae or heavy sediment you do not want to pass through the filter, or when you need to lower the pool water level quickly. You will lose pool water in the process, so have the hose ready to refill. Use RECIRCULATE when you want to keep that water in the pool and simply move it around. For vacuuming on a sand system, our guide on how to vacuum a pool with a sand filter covers when to vacuum on FILTER versus WASTE.

Safety: Never Move the Valve With the Pump Running

This is the single most important rule for any multiport valve. Always turn the pump off before changing the valve position, then turn it back on once the handle is locked into the new setting.

Moving the diverter while water is under pressure tears the spider gasket, the soft rubber part that seals each port. A torn gasket lets water leak between ports, which most often shows up as unfiltered water reaching the pool or water running out the waste line even on FILTER. It can also blow the handle past its detent. If your valve has started leaking between positions, a worn or shredded multiport valve spider gasket is the usual cause and is a common repair. A persistent leak to waste, or pressure that will not come down, is also covered in our guide on pool filter pressure too high.

The off-pump rule applies to every position, RECIRCULATE included. Build the habit and the valve will last for years.

Related Guides

• Pool Filter Valve Settings Guide - every multiport position explained in depth
• How to Backwash a Pool Filter - all multiport valve positions in the backwash process
• How to Backwash a Sand Filter - the full step-by-step sequence
• How Often to Backwash Pool Filter - the PSI method
• Why Is My Pool Filter Not Working - using recirculate to diagnose pump vs filter
• Backwashing Complete Guide - all backwash topics