Pentair 170021 FNS Plus Tank Lid — 48 sq. ft. D.E. Filter (FNSP48), Genuine OEM
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The Pentair 170021 Tank Lid is the genuine OEM replacement lid for the 48 sq. ft. FNS Plus vertical grid D.E. filter (FNSP48). The lid seals the upper half of the filter tank against system pressure, and is the part to replace when cracking, crazing or a distorted sealing surface causes leaks at the tank band.
Key Features
- Genuine Pentair OEM part: Listed as item 26 on Pentair's FNS Plus vertical grid filter parts schematic.
- Correct size: Specific to the 48 sq. ft. FNSP48 filter — lids are not shared across tank sizes.
- Pressure-rated moulding: Built to hold the filter's operating pressure across seasons of chemical and UV exposure.
- Restores a leaking tank: Addresses seepage at the clamp band caused by a damaged or warped lid.
- Tank half only: A targeted repair instead of replacing the complete filter.
Specifications
- Part Number: 170021
- Type: Filter tank lid (upper tank half)
- Filter Size: 48 sq. ft.
- Fits: Pentair FNS Plus vertical grid D.E. filter, model FNSP48
- Schematic Reference: Item 26
- Supplied As: Lid only — clamp band, o-ring, grids and manifold sold separately
- Brand: Pentair (Genuine OEM)
Frequently Asked Questions
Will this fit my 36 or 60 sq. ft. FNS Plus filter?
No. Each tank size uses its own lid. The 36 sq. ft. FNSP36 takes part 170020 and the 60 sq. ft. FNSP60 takes 170022. Check the model number on your filter label before ordering.
Does it include the clamp band or o-ring?
No. This is the lid only. The bulkhead o-ring and clamp band are separate parts.
How do I know the lid is the problem?
Typical signs are water seeping from the seam at the clamp band after the o-ring has been replaced, visible cracking around the moulding, or a lid that will not seat evenly when the band is tightened.
Is any special tool needed?
No. The filter must be depressurised and the clamp band removed first — always relieve pressure at the air relief valve before opening a filter tank.
Frequently asked questions
What size filter do I need?
Filter area is matched to pump flow rate, not to pool volume alone. An oversized filter runs longer between cleanings and puts less back pressure on the pump, which is why installers routinely size up rather than to the minimum.
What is the part number for this filter?
Pentair lists this filter under part number 170021. Quote 170021 when you cross-reference against your equipment manual, an existing part, or a parts diagram, so you are comparing the same revision.
How do I know when to clean the filter?
Note the pressure on a clean filter, then clean when the gauge climbs roughly 8 to 10 PSI above that baseline. Cleaning on a fixed calendar instead of the gauge either wastes effort or lets flow drop far enough to strain the pump.
How do I confirm this fits my equipment?
Match the part number stamped on the component you are replacing, or look it up in the parts list for your Pentair equipment. If your model or serial number is not named on this page, send it to us before you order and we will confirm the fit.
Does this listing include the internal filter elements?
Check the specification section above. Filter tanks are sold both complete and as bodies without cartridges, grids or laterals, and those internals are a significant part of the replacement cost.
Is there a warranty on this filter?
It carries the standard Pentair manufacturer warranty. The terms are set by Pentair, and on some equipment the coverage only applies when a licensed professional performs the installation. Keep the receipt and packaging until you have confirmed correct operation.