Domakihub Replace a Pool Multiport Valve Spider Gasket in 1 Hour
A worn spider gasket wastes water and wrecks filter performance — here is how to diagnose and fix it for about €15.
Reviewed by Domakihub pool pros · 2026-06-23 · 5 min read
If water is bleeding out through your backwash line while the multiport valve is set to Filter, the culprit is almost always a cracked or compressed spider gasket — the star-shaped rubber seal inside the valve that routes water to the correct port. The video above walks through the full replacement on a Pentair multiport valve, and this guide adds every step in plain language so you can follow along confidently. Whether you manage a private villa, a holiday rental, or a hotel pool in Greece, this is a repair you can complete in under an hour with basic tools and a gasket that costs a fraction of a service call.
What Is a Spider Gasket and Why Does It Fail?
The spider gasket sits inside the top body of your multiport valve — the rotating hub you turn to switch between Filter, Backwash, Rinse, and other modes. It forms a pressure seal across six or eight radial channels, directing water only to the port your handle is pointing at. Over time, the rubber hardens, cracks along the ribs, or compresses unevenly, leaving gaps that water exploits.
In Greece the combination of high summer temperatures, intense UV radiation around uncovered equipment pads, and extended off-season shutdown cycles accelerates rubber degradation. Most gaskets last three to seven years under normal conditions; a cheap replacement gasket bought from any pool-supply shop or online marketplace is all you need to restore a fully sealed valve.
Diagnosing the Spider Gasket Before You Disassemble Anything
The classic symptom is a steady trickle or stream of water exiting the backwash port even when the valve is firmly set to Filter — sometimes visible as a damp patch on the ground near the waste line. A secondary sign is loss of return-jet pressure in the pool, since some water is bypassing the filter and escaping instead of being pushed back through the returns.
Before ordering a part, confirm the diagnosis: turn the system off, remove the valve handle and the retaining ring on top, and shine a torch into the valve body. If you can see flat spots, cracks running along the ribs of the gasket, or sections that look compressed and shiny rather than plump and matte, replace it. If the gasket looks intact, inspect the valve body itself for hairline cracks before assuming the gasket is the problem.
How to Replace the Spider Gasket — Step by Step
- 1
Shut down the pump and relieve pressure
Switch the pump off at the breaker, not just the controller, so it cannot start accidentally. Turn the multiport handle to Recirculate or Winterize to relieve any residual line pressure, then close the skimmer and return valves if your plumbing has isolation points. Place a bucket or towel under the valve — some water will drain out when you open the top.
- 2
Remove the valve top and expose the spider gasket
Unscrew or unclip the handle assembly, then undo the large collar or union ring that holds the valve top to the body — it is usually hand-tight after years of use, but a rubber strap wrench helps if it is stuck. Lift the top straight off. You will see the spider gasket sitting in a machined channel in the valve body. Take a photo before you touch anything so you can confirm the orientation when fitting the new one.
- 3
Pull out the old gasket and clean the channel
The gasket often lifts out in one piece; if it has deteriorated it may come out in sections. Use a flathead screwdriver or a plastic pick to remove every fragment — do not leave rubber debris in the channel. Wipe the channel and the mating surface on the valve top with a clean cloth dampened with isopropyl alcohol, removing old lubricant, algae residue, and grit. A clean seating surface is essential for a leak-free repair.
- 4
Seat the new gasket and apply silicone lubricant
Press the new spider gasket firmly into the channel, starting at one rib and working around the star shape so it sits flat and even with no lifted edges. Apply a thin, even coat of silicone-based pool lubricant (never petroleum jelly, which degrades rubber) to the top face of the gasket and to the mating surface in the valve top. This lubricant lets the valve rotate smoothly and extends gasket life significantly — a common omission that causes premature wear.
- 5
Reassemble, test, and check for leaks
Lower the valve top back onto the body, aligning any locating tabs or notches, and tighten the collar ring firmly by hand. Reattach the handle. Open isolation valves, restart the pump, and set the valve to Filter. Watch the backwash port for 60 seconds — it should be completely dry. Then cycle through each valve position (Backwash, Rinse, Recirculate) to verify the handle turns without grinding and that flow goes where it should. If any port still leaks, recheck that the gasket is seated flat with no folded edges.
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FAQ
- How do I know which spider gasket to buy for my multiport valve?
- The easiest route is to note the brand and model number printed on the valve body — Pentair, Hayward, Praher, and Astral each use different gasket profiles. Search the model number on any pool-supply site and buy the OEM or an OEM-equivalent replacement. If you cannot find a model number, measure the outer diameter of the gasket channel in millimetres and confirm the number of ribs (usually 6 or 8) before ordering.
- Can I use any lubricant, or does it have to be silicone?
- It must be a silicone-based lubricant specifically rated for pool equipment. Petroleum-based products (Vaseline, WD-40, general grease) cause rubber to swell and degrade rapidly, which will ruin your new gasket within one season. A small tube of Magic Lube or equivalent costs around €5 and lasts for years — keep it on hand for o-rings and pump lid seals too.
- My valve still leaks to the backwash port after replacing the gasket — what else could be wrong?
- First confirm the gasket is seated perfectly flat with no lifted or folded ribs; even a small gap is enough to allow bypass. If the gasket looks correct, inspect the valve body and top for cracks — particularly around the port openings — which no gasket replacement can fix. Also check that the handle is firmly engaging the rotor and not stopping just short of the detent position, which would leave two ports partially open simultaneously. If the valve body is cracked, replacement of the full valve head is the only permanent solution.