Pentair Siata 2250 Twin Pilot Piston Assembly

This twin pilot piston assembly is the genuine Pentair part for the Siata 2250 control valve, supplied by WrekinWater as part number 0402012758. It's the moving component that shifts within the valve body under pilot pressure to route water through each stage of the regeneration cycle. Fitting a fresh assembly restores clean, leak-free shifting where the original piston or its seals have worn.

Signs you need this part

• Water is leaking continuously to drain rather than only during a regeneration.
• Untreated water seems to bypass the resin bed even though the valve is cycling.
• You hear a popping or clunking noise as the valve changes between positions.
• The piston feels stuck or reluctant to shift when a manual cycle is triggered.

The twin pilot piston is effectively the heart of the Siata 2250 valve, sliding within the body under pilot pressure to switch between service, backwash, brine draw and rinse. As its seals wear, water starts to pass between positions that should be sealed off from each other, which shows up as continuous drain flow, wasted salt and water, or hardness bleeding through even when the valve appears to be cycling normally.

WrekinWater, a family run business based in Bettisfield, Shropshire with an Excellent Trustpilot rating built over 15 years and more than 50,000 customers served, stocks genuine Pentair Siata parts including this piston assembly.

How to fit it

1. Turn off or bypass the water supply and relieve pressure before opening the valve.
2. Remove the pilot assembly or valve cover to access the piston.
3. Withdraw the old piston assembly from the valve body.
4. Lightly lubricate the seals on the new piston assembly with a food-safe silicone grease.
5. Insert the new piston into the valve body and refit the cover or pilot assembly.
6. Restore the water supply and run a manual cycle to confirm smooth shifting with no leaks.