Product Overview

The Pentair FNS Plus Tank Lid Assembly 48 sq ft | 170021 is a genuine Pentair replacement tank lid designed for the Pentair FNS Plus FNSP48 48 sq ft D.E. pool and spa filter. This replacement lid helps restore the filter’s sealing surface, pressure integrity, and safe operation when the original lid is cracked, damaged, worn, or no longer sealing properly.

Built from fiberglass-reinforced polypropylene, this lid is designed for strength, chemical resistance, and durability in pool equipment environments. It is commonly listed for use with the FNS Plus 48 sq ft vertical grid D.E. filter and is identified with UPC 788379670818.

Ideal For

• Pentair FNS Plus FNSP48 filters
• 48 sq ft D.E. pool and spa filters
• Replacing cracked or damaged filter lids
• Restoring proper tank sealing
• Filter tank repairs
• Pool equipment pad service work
• D.E. filter maintenance
• Professional pool service technicians
• OEM filter part replacement
• Residential pool filtration systems

Key Features

• Genuine Pentair replacement part — OEM lid assembly designed for compatible FNS Plus filters.
• Fits FNS Plus 48 sq ft filter — made for the Pentair FNSP48 D.E. filter model.
• Restores tank sealing — helps maintain proper filter pressure and leak-free operation.
• Fiberglass-reinforced polypropylene construction — strong, chemical-resistant material built for pool equipment environments.
• Tan / cream finish — matches compatible FNS Plus filter tank assemblies.
• Designed for D.E. filtration systems — supports safe operation of vertical grid D.E. filters.
• Service replacement solution — replaces only the tank lid instead of the complete filter when the bottom tank and internal components are still usable.
• OEM fit and function — designed to match supported Pentair filter part diagrams.
• Pressure-system component — critical part for safe filtration operation.
• Professional service part — recommended for qualified pool equipment repair and installation.

Benefits

The Pentair 170021 tank lid assembly helps restore safe, dependable operation to compatible FNS Plus 48 sq ft D.E. filters. A damaged lid can cause leaks, poor sealing, pressure loss, unsafe operation, or difficulty keeping the filter properly clamped.

Replacing the lid with the correct OEM part helps maintain the filter’s original design fit and pressure-rated sealing performance. This is especially important because pool filters operate under pressure and must be assembled with the correct lid, clamp, O-ring, and tank components.

For pool professionals, the 170021 is a practical repair part for extending the service life of a compatible FNS Plus FNSP48 filter without replacing the entire filter system.

Specifications

Included Components

• 1 × Pentair 170021 FNS Plus 48 sq ft tank lid assembly

Filter bottom tank, clamp band, tank O-ring, internal grid assembly, manifold, pressure gauge, air relief valve, drain assembly, D.E. powder, plumbing fittings, and installation labor are sold separately unless specifically included by the supplier.

Compatibility Notes

This tank lid assembly is designed for the Pentair FNS Plus 48 sq ft D.E. filter, commonly referenced as FNSP48.

Common compatibility references include:

• Pentair FNS Plus FNSP48
• Pentair FNS Plus 48 sq ft D.E. filter
• Pentair filter tank bottom assembly 170017, where applicable
• Replacement applications requiring part 170021
• Older PacFab / Pentair FNS Plus 48 sq ft filter lid replacement applications where confirmed by part diagram

Always confirm the filter model number, tank size, filter label, clamp style, lid part number, tank bottom compatibility, and parts diagram before ordering. This lid is not universal for all FNS Plus filter sizes.

Installation Notes

This lid should be installed by a qualified pool professional. Pool filters operate under pressure, and incorrect assembly can create serious safety hazards.

Before servicing the filter, turn off the pump, shut down all related equipment, and fully relieve system pressure using the air relief valve. Inspect the tank O-ring, clamp band, tank bottom, sealing surfaces, and air relief assembly before reassembly.

Never operate the filter with a damaged clamp, damaged O-ring, cracked tank component, or improperly seated lid. After installation, restart the system carefully, bleed air from the filter, check for leaks, and verify normal operating pressure.

Customer-Facing Q&A

Q: What is the Pentair 170021?
A: It is a genuine Pentair replacement tank lid assembly for the FNS Plus 48 sq ft D.E. filter.

Q: What is the SKU?
A: The SKU is 170021.

Q: What is the UPC / barcode?
A: The UPC / barcode is 788379670818.

Q: What filter does this fit?
A: This lid fits the Pentair FNS Plus FNSP48 48 sq ft D.E. filter.

Q: Is this for a cartridge filter?
A: No. This part is designed for the FNS Plus D.E. filter.

Q: What material is the lid made from?
A: It is made from fiberglass-reinforced polypropylene.

Q: What color is the lid?
A: The lid is commonly listed as tan / cream.

Q: Does this include the complete filter?
A: No. This listing is for the tank lid assembly only.

Q: Does this include the clamp or tank O-ring?
A: No, unless specifically supplied by the seller packaging. Verify contents before fulfillment.

Q: Does this fit all FNS Plus filters?
A: No. This lid is specifically for the 48 sq ft FNS Plus model. Other FNS Plus filter sizes use different parts.

Q: Should this be professionally installed?
A: Yes. Professional installation is strongly recommended because pool filter tanks operate under pressure and must be assembled correctly for safe operation.