Fleck 9100SXT twin-tank alternating softener valve: quick sheet

Covers: Fleck 9100 valve with the SXT electronic timer on two resin tanks that take turns (alternating twin), 3/4 in. or 1 in. meter, sold since the 2000s under many dealer and online brands (e.g. Aqualux and Applied Membranes packages, 1.0 to 3.0 cu ft per tank). The older 9100 with a mechanical 3200 timer shares the valve body but not the electronics. Valve and serial label are on the valve/power head; the tank in service is shown both on the SXT display (U1/U2) and by a physical indicator on the valve. Search terms: Fleck 9100SXT, 9100 SXT twin, alternating softener, Fleck twin tank Err 0, 9100 tank in service, 9100SXT programming.

Cross-checkedBrands: Fleck, Pentair7 components

One valve, two resin tanks, one brine tank. One tank is always in service while the other waits in standby, so the house never gets hard water during regeneration. A meter counts gallons; when the tank in service reaches its programmed capacity the valve switches service to the standby tank right away and regenerates the exhausted tank, then parks it in standby. Because the regenerating tank is fed by the other (soft) tank, regeneration uses soft water. The SXT face is the same three-button controller used on the 5600SXT and 7000SXT (Extra Cycle, Up, Down), but on a twin it must be set to two tanks and meter-immediate control.

Safety first

Unplug the transformer before opening the power head; moving gears can pinch.
Put the valve in bypass and open a downstream faucet to relieve pressure before removing the power head, piston or injector cap; disassembly under pressure floods the area.
Do not let the unit freeze; a frozen valve body can crack.
Do not use the softener on water that is microbiologically unsafe or untested; it is not a disinfection device.

How it works

Service: hard water goes down through the resin of the tank in service and up the riser to the outlet; calcium and magnesium are swapped for sodium on the resin.

When the calculated capacity (unit capacity divided by hardness, minus any reserve) is used up, the control starts regeneration immediately (control type FI). Pentair states twin 9100 systems must use meter-immediate; delayed and time-clock modes are not for this valve.

Standard twin regeneration (dF1b, single backwash, downflow): backwash, brine draw and slow rinse, rapid rinse, then brine tank refill. During refill treated water is already available at the outlet. Each step can be set from 0 to 199 minutes; a 0 skips the step.

The display alternates between time of day, gallons remaining and the tank in service (U1 or U2). The flow indicator flashes whenever the meter sees outlet flow, which is the quickest way to prove the meter works.

On power loss the SXT keeps settings in permanent memory and holds the time for a limited period (Pentair's two documents give 24 h and at least 48 h); if power drops mid-regeneration the valve stays where it is and resumes when power returns.

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Official manufacturer documentation

Always confirm values against the tech sheet for the exact model.

OnCall Tech is a reference tool for trained technicians and can make mistakes. Always disconnect power and confirm with the manufacturer's documentation before you work. © 2026 OnCall Tech. Original content; not a reproduction of any manufacturer document.Generic part photos (not of this brand): Water softener resin tank with its control valve next to a storage tank by రవిచంద్ర (Ravichandra), CC BY-SA 4.0

Diagnostic guides for this appliance

Guide · Water Softener

Water softener and under-sink RO annual service: salt, brine tank, resin, filters and tank charge

A softener needs a monthly salt check (WQA: refill when under half full), periodic brine tank cleaning, breaking any salt bridge and, on iron or bacteria-prone water, a resin cleaner used per the manufacturer. An RO system needs pre-filter changes roughly every 6-12 months, the membrane every few years depending on feed water, a yearly sanitize at filter change and a tank air charge check with the tank empty. Intervals vary by maker; the model manual wins.

7 steps ~60 minmoderate

Guide · Water Softener

Water feels slippery or 'won't rinse off' after a softener install

A slick feel is the normal sign that hardness minerals are gone; soap rinses differently and people tend to use more of it in soft water. It is not a fault. Rule out real problems (salty taste, softener stuck in brine) and, if the customer dislikes the feel, adjust the blend or bypass setting on valves that have one, after a hardness test.

4 steps ~20 mineasy

Guide · Water Softener

Water softener noises during regeneration: normal vs fault

A regeneration cycle is noisy by design: the valve motor hums and clicks as it steps through positions, water rushes to the drain, and brine is drawn through the resin. That is normal as long as it ends when the cycle ends (typically a couple of hours). Noise that goes on for hours, runs outside regeneration, or sounds like grinding or banging points to a stuck valve, a clogged brine line, worn parts or a water pressure problem.

5 steps ~30 mineasy

Other water softeners & filters manuals

Manual · Water Softener

Kinetico non-electric twin-tank softeners (Premier Series, Premier XP, Signature Series): quick sheet

Kinetico water-powered twin-tank softeners: Premier Series softeners and the 4040s/4060s Overdrive combination units (carbon, Chloraban or Macrolite RX); older 2030s/2060s-era units follow the same non-electric principle but were not researched here, Premier XP (S150, S250, S250 OD, S350, S550, S650, S650 OD, Q850 XP and Q850 OD XP), and Signature Series 735 and 935. Sold and serviced through authorized local Kinetico dealers. Model and meter disc number are on the dealer's data sheet/owner's manual record page; the control valve with the regeneration indicator dot sits on top of the two resin tanks. Search terms: Kinetico not soft, Kinetico manual regeneration screwdriver, Kinetico running constantly, Kinetico brine tank full of water, Kinetico bypass yellow green red.

6 components7 common failuresKinetico

Manual · Water Softener

Culligan home softeners (HE / HE Twin with Aqua-Sensor or Soft-Minder, Medallist Series): quick sheet

Dealer-sold Culligan residential softeners: Culligan HE (High Efficiency) 1 in. softeners in 9, 10, 12 and 14 in. tanks, downflow and upflow, with Soft-Minder meter or Aqua-Sensor resin probe (owner's guides 2019-2021); HE Twin, HE Twin Upflow and outdoor versions; HE Municipal; and the Medallist Series 8 in. and Medallist Plus 30/45/60 (Accusoft four-key timer, 3/4 in. or 1 in. 5-cycle valve). Media tank serial number is on the top of the tank; control model/serial and settings are on the 'Important Data' page the dealer fills in. Search terms: Culligan HE problem found, Culligan Aqua-Sensor, Culligan regen now, Culligan Medallist REG light, Cul-Flo-Valv bypass blue knob.

6 components7 common failuresCulligan

Manual · Water Softener

Waterdrop G3P600 tankless under-sink RO system: quick sheet

Waterdrop WD-G3P600 tankless reverse osmosis (600 GPD, 2:1 pure to drain), with the smart TDS faucet and three twist-in cartridges: WD-G3-CF (sediment + carbon block), WD-G3-CB (activated carbon post filter) and WD-G3P600-RO (membrane). Sold online and at home centers since about 2021; an upgraded version and a remineralization version use the same layout. Model is printed on the housing and manual cover; made by Qingdao Ecopure Filter Co. Search terms: Waterdrop G3P600 E02, E03, E04, G3P600 red light reset, Waterdrop tankless RO no water, G3P600 high TDS, G3P600 beeping.

7 components8 common failuresWaterdrop