How to Backwash a Hayward Pool Filter — Sand & DE Models

Hayward Filter Models This Guide Covers

This guide applies to all Hayward ProSeries sand filters:

• S166T (16 inch), S180T (18 inch), S210T (21 inch)
• S244T (24 inch), S270T (27 inch), S311T (30 inch)
• Hayward ProSeries High-Rate Sand Filters (all sizes)
• Hayward DE filters: DE2420, DE3620, DE4820, DE6020, DE7220

The backwash procedure is identical across all ProSeries models. The only difference is that DE filters require replenishing DE powder after every backwash — covered in the DE-specific section below.

Before You Start: The One Rule That Prevents Valve Damage

Always turn the pump off before moving the multiport valve.

This is not a suggestion — it is the most common cause of cracked Hayward valve bodies. Hayward’s multiport valve contains a rubber spider gasket that seals each port. When you rotate the handle under pump pressure, this gasket is sheared. The result: a $100–$200 repair that is completely avoidable.

After turning off the pump, wait 5–10 seconds for the internal pressure to bleed off before touching the handle.

Step-by-Step Backwash Procedure

Follow the steps in the How-To section above. Here are the most important details expanded:

Reading the Hayward Sight Glass

The sight glass is the small clear oval window on the elbow of the backwash port (the port your backwash hose connects to). When backwashing is working correctly:

• First 30–60 seconds: Dark brown or grey water — this is the trapped debris flushing out
• Next 60–90 seconds: Gradually clearing
• When clear: Stop the backwash

If the sight glass clears in under 30 seconds, the sand has channelled and water is bypassing the filter bed rather than flushing debris from it. See our guide on how often to change pool filter sand for the full list of signs that sand needs replacing.

The Hayward Valve Handle Lock

Some Hayward multiport valves have a small push-and-rotate lock mechanism to prevent accidental valve movement during operation. If your valve handle does not rotate easily:

1. Make sure the pump is fully off and pressure has bled off
2. Press the handle down slightly while rotating (the lock releases under downward pressure)
3. If still stiff, the O-ring on the internal port disc may need lubricating — apply pool-safe O-ring lubricant (not petroleum-based products) via the valve cover

After Backwash: Always Run RINSE

The RINSE step is the one most Hayward owners skip, then wonder why sand appears in their pool after backwashing.

The RINSE position on Hayward valves runs water through the filter in the normal direction (top to bottom) for 30 seconds before returning to FILTER. This re-settles the sand bed into a compact, flat layer after the reversed backwash flow has disturbed it.

Without RINSE, loose sand near the top of the filter bed returns to the pool through the return jets within the first minute of normal operation.

Hayward DE Filter: Additional Step After Backwashing

If you have a Hayward DE filter (DE2420, DE3620, etc.), there is one additional step after the backwash that sand filter owners do not need to do: replenishing the DE powder.

Hayward DE filters use diatomaceous earth powder coated on fabric grids as the actual filter medium. Backwashing strips most of this coating off the grids. Without fresh DE, the grids filter poorly.

After every backwash on a Hayward DE filter:

1. Complete the full backwash and RINSE procedure above
2. Calculate your filter’s DE requirement (approximately 80% of the rated total capacity — check your DE filter manual)
3. Mix the DE powder with water to form a slurry in a bucket
4. With the pump running on FILTER, pour the slurry slowly into the skimmer
5. Run the pump for a few minutes to allow the DE to coat the grids evenly

For exact DE quantities and the full procedure, see our how to backwash a DE filter guide.

When Backwashing Is Not Enough

Backwashing removes trapped debris from the sand, but it cannot remove the oils, sunscreen residue, and mineral buildup that accumulates in the sand over months of use. Once per season, run a chemical filter cleaner through the system — added to the skimmer, soaked overnight, then backwashed out. This dissolves the grease and oil that backwashing misses and is the single most effective way to extend your sand’s life.

If backwashing no longer brings pressure back to your clean baseline, or the water stays cloudy despite correct chemistry, it may be time to change the pool filter sand.

Related Guides

• How to Backwash a Pool Filter — general backwash guide for all filter types
• How Often to Backwash Pool Filter — the PSI-based frequency rule
• How to Change Pool Filter Sand — when sand replacement is needed
• Backwashing Complete Guide — all backwash topics