How to Backwash a Pentair Pool Filter - Triton and FNS Models
Pentair Triton II sand filters and FNS DE filters use a top-mount multiport valve with the same 7 positions as most pool filters. This guide walks through the exact backwash procedure for both, including the correct valve positions and the DE recharge step.
Pentair Filter Models Covered
This guide applies to:
- Pentair Triton II (TR-40, TR-60, TR-100, TR-140) - the most common Pentair sand filter line for residential inground pools
- Pentair Sand Dollar (SD-40, SD-60, SD-80) - popular for smaller inground and large above-ground installations
- Pentair FNS Plus (36, 48, 60) - DE filters using the same multiport valve configuration
- Pentair Clean and Clear Plus - cartridge filters do not backwash; see the cartridge cleaning guide instead
The Key Rule for All Pentair Filters
Always turn the pump off before moving the multiport valve.
This applies to every pool filter brand, but it is worth emphasizing for Pentair filters because the Triton II is a common first filter for many pool owners who did not receive a proper orientation when the pool was installed.
Moving the Pentair multiport valve while the pump is running cracks the internal spider gasket and can split the valve body. Replacement spider gaskets cost $20-40 and require disassembling the valve. A replacement valve body costs $80-150. The fix takes the pump out of service for a day. All of this is 100% avoidable by turning the pump off first.
Pentair Multiport Valve Positions
Pentair top-mount valves have the same six positions found on Hayward and most other residential filters:
| Position | Function |
|---|---|
| FILTER | Normal operation - water through sand, returns to pool |
| BACKWASH | Reversed flow to flush out debris |
| RINSE | 30-second re-settle after backwash |
| WASTE | Bypasses filter, water exits pool |
| RECIRCULATE | Bypasses filter, water returns to pool |
| CLOSED | Shuts all flow |
The WINTERIZE position (between settings) is available on some Pentair models - used for pool closing in freeze climates.
How Much DE After Backwashing a Pentair FNS Filter
| FNS Plus Model | Full Charge | After Backwash (80%) |
|---|---|---|
| FNS Plus 36 | 4.5 lbs | 3.6 lbs |
| FNS Plus 48 | 6 lbs | 4.8 lbs |
| FNS Plus 60 | 7.5 lbs | 6 lbs |
Always verify against the label on your specific filter - Pentair prints the exact DE capacity on the filter housing.
Replacing the Pentair Multiport Valve O-Ring
The large O-ring at the base of the Pentair multiport valve (where it connects to the filter tank) should be lubricated annually with pool-safe silicone lubricant. Dry O-rings crack and cause valve-to-tank leaks.
Do not use petroleum-based lubricants - they degrade rubber. Pool silicone lubricant is specifically formulated for this use.
Pool silicone O-ring lubricant on Amazon
Related Guides
- How to Backwash a Pool Filter - complete general backwash procedure
- How to Backwash a Hayward Pool Filter - Hayward-specific steps
- How Often to Backwash Pool Filter - the PSI method
- Backwashing Complete Guide - all backwash topics
Frequently Asked Questions
How do I backwash a Pentair Triton II sand filter?
Where is the backwash port on a Pentair filter?
How often should I backwash my Pentair pool filter?
My Pentair filter pressure is still high after backwashing - what do I do?
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