Buying Guides — Toilet Parts

Toilet Fill Valve Buying Guide: Which to Buy in 2026

Everything you need to choose the right fill valve for your toilet tank, covering valve types, compatibility, water efficiency, noise, and the top-rated models from Fluidmaster, Korky, TOTO, and more.

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Flushing power and MaP flush-test scores
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Brand reliability and warranty

Research updated June 2026.

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Quick Answer

For most toilets, the Fluidmaster 400AH is the single best fill valve to buy in 2026. It fits virtually any 2-inch shank toilet, installs in under 10 minutes, self-adjusts water levels, and its anti-siphon design meets every current plumbing code requirement.

The fill valve is the component inside your toilet tank that controls how water refills after each flush. When it wears out, you get a running toilet, slow fill times, noisy hissing, or ghost flushing that wastes thousands of gallons per year. Replacing a fill valve is one of the most cost-effective plumbing repairs you can make, and choosing the right replacement makes the difference between a quiet, reliable tank and another service call in six months.

This guide covers every fill valve type, what the specifications actually mean, which brands produce consistently reliable parts, and which specific models are worth buying for standard toilets, low-flow toilets, pressure-assist systems, and older ballcock installations.

What are the different types of toilet fill valves?

There are four main types: the traditional ballcock (float ball on a horizontal arm), the modern float-cup fill valve (plastic cylinder with a floating cup that rides up and down the shaft), the floatless (bottom-entry) fill valve, and the diaphragm fill valve. Float-cup fill valves dominate the market today because they are compact, adjustable, quiet, and compatible with low-water tanks down to 1.0 GPF. Ballcocks are largely obsolete and found only in older toilets.

Float Ball (Ballcock)

The original fill valve design uses a rubber ball attached to a horizontal metal or plastic arm. As the tank fills, the ball rises with the water level and eventually shuts off the flow. Ballcocks are durable but bulky, prone to mineral buildup on the diaphragm seat, and they take up a large portion of the tank. Replacement ballcocks are available for legacy toilets, but most homeowners upgrade to a float-cup valve at the same time.

Float-Cup Fill Valve

The dominant design since the 1990s. A plastic cylinder sits vertically in the tank, and a floating cup rides the outside of the shaft. Water refill stops when the cup reaches a preset height. These valves are compact, fit tanks from older 3.5-gallon designs down to modern 1.0 GPF tanks, and allow precise water-level adjustment by pinching a clip or turning a screw. The Fluidmaster 400A and its updated variants are the most-installed float-cup valves in North America.

Floatless (Bottom-Entry) Fill Valve

Instead of a floating mechanism, these valves use a pressure-sensing diaphragm at the bottom of the tank. There are no moving parts visible above the waterline, which makes them exceptionally quiet and nearly invisible inside a tank. They are sometimes called "fill valves with no float" and are well-suited to very shallow tank designs. The Fluidmaster 400LS is one widely available floatless model.

Diaphragm Fill Valve

Used primarily in pressure-assist toilet tanks (such as the Flushmate system), the diaphragm valve is a sealed, pressurized unit. It is not interchangeable with gravity-flush tank fill valves. If you own a Flushmate-equipped toilet, you must source parts directly from the pressure-assist tank manufacturer. Standard replacement fill valves will not work and can cause tank failure.

What specifications matter most when buying a fill valve?

The three most important specifications are shank length (must match your tank depth, typically 7 to 14 inches adjustable), connection size (nearly universal at 7/8-inch tank hole for gravity-flush toilets), and flow rate (measured in gallons per minute). A fill valve with a high GPM rating refills the tank faster, which matters most in high-traffic bathrooms. Anti-siphon certification and EPA-compliant construction are also required by most municipal codes.

Shank Length and Adjustability

Most modern fill valves offer an adjustable shank ranging from about 7 to 13 or 7 to 14 inches. This covers the vast majority of one-piece and two-piece toilet tanks. However, very shallow one-piece tanks (common in TOTO and some Kohler designs) sometimes require a dedicated short-shank valve. Always measure from the bottom of the tank to the top of the overflow tube before ordering a replacement. If your existing valve barely clears the lid, an adjustable valve with a minimum compressed height below 8 inches is essential.

Flow Rate

Fill valve flow rate is typically listed in gallons per minute (GPM). Entry-level valves refill at roughly 1.5 to 2.0 GPM. Better-quality valves push 3.0 GPM or more. In a busy household bathroom, a faster fill rate means the toilet is ready for the next use sooner and water flow noise is brief. The Fluidmaster 400AH is rated at approximately 3.0 GPM. Korky's QuietFILL Platinum models are rated similarly.

Water Level Adjustment Range

The fill valve determines where water stops in the tank, and the water level directly affects flush performance. Too low and your toilet under-flushes. Too high and water creeps into the overflow tube, creating a constant slow leak. Look for a valve that allows at least a 2-inch vertical adjustment range and holds the preset level firmly without drifting over time. Clip-style adjusters (Fluidmaster) and screw-top adjusters (Korky) both work well when the locking mechanism is robust.

Anti-Siphon and Code Compliance

All fill valves installed in the United States must include an anti-siphon mechanism that prevents tank water from backflowing into the supply line. This is a plumbing code requirement in all 50 states. Every fill valve listed in this guide carries an anti-siphon feature, so compliance is not an issue with major brands. If you are replacing a very old ballcock that lacks this feature, the upgrade to any modern fill valve immediately brings you into code compliance.

Material Quality and Longevity

Fill valve bodies are typically made from glass-filled polypropylene or ABS plastic. Valves at the low end use thin-wall injection-molded components that can warp or crack under the constant humidity of a toilet tank. Premium valves use thicker engineering-grade plastic and stainless steel adjustment screws. TOTO's genuine replacement fill valves use materials compatible with the Cefiontect-coated tank surfaces and are engineered to the same tight tolerances as the original equipment.

Expert Take

A fill valve failure that causes continuous running can waste 200 gallons of water per day according to published EPA estimates. Given that a quality replacement fill valve costs under $20 at most retailers and installs without special tools, deferring the repair because it seems minor is one of the most expensive choices a homeowner can make. The payback on a new fill valve is typically measured in weeks, not months.

Which fill valve brands are most reliable?

Fluidmaster and Korky are the two dominant aftermarket brands, and both produce fill valves that routinely earn 4.5-star or higher ratings across thousands of owner reviews. Fluidmaster's 400-series is the most-installed aftermarket fill valve in the world. Korky's QuietFILL line specifically targets noise reduction. For TOTO toilets, TOTO's own replacement parts (part numbers matching the original) are strongly preferred because proprietary tank geometry can make aftermarket valves difficult to adjust.

Fluidmaster

Fluidmaster, founded in 1957 and based in San Juan Capistrano, California, holds more U.S. patents related to fill valve design than any other manufacturer. The 400A introduced the float-cup concept that every competitor has since copied. The updated 400AH adds a height-adjustable body collar. The PRO45 and PRO550 lines target professional installers and whole-house water efficiency programs. Fluidmaster parts are stocked at virtually every plumbing supply house, hardware store, and home center in the country.

Korky

Made by Lavelle Industries in Burlington, Wisconsin, Korky fill valves are a strong alternative to Fluidmaster, particularly for homeowners troubled by valve noise. The Korky 528MP QuietFILL Platinum is engineered with an internal tower that significantly dampens water entry sound compared to standard float-cup designs. Korky also produces specialty valves for Mansfield, Eljer, and some older toilet brands that use non-standard shank sizes.

TOTO OEM Parts

TOTO's replacement fill valves carry the same part numbers as the original equipment in Drake, Drake II, UltraMax II, Aquia IV, and other TOTO toilet lines. TOTO tanks use a specific overflow tube height and float-cup geometry that aftermarket valves can sometimes conflict with, resulting in incorrect water levels or intermittent fill cycles. If you own a TOTO toilet, confirming the correct TOTO part number before ordering an aftermarket substitute is worth the extra few minutes.

American Standard and Kohler OEM

American Standard and Kohler both supply branded fill valves for their own toilets including the Champion 4, Cadet 3, Highline, and Cimarron series. These OEM parts maintain the designed fill rate and water level for the flush system as calibrated at the factory. That said, the Fluidmaster 400AH is a documented compatible replacement for most Champion 4 and Cadet 3 tanks, and American Standard's technical documentation acknowledges this.

Expert Take

Across aggregated owner reviews from verified purchasers, Fluidmaster's 400-series shows a lower return and complaint rate than nearly every private-label fill valve sold under home center house brands. The price difference between a name-brand Fluidmaster or Korky valve and a no-name import is typically two to four dollars. That four dollars buys meaningful quality assurance in a part that can cause hundreds of dollars in water damage if it fails.

How do you know if your fill valve needs to be replaced?

The clearest sign is a toilet that runs continuously or cycles on periodically without being flushed (ghost flushing caused by water draining into the overflow tube). Other indicators include a hissing or whistling sound during or after filling, a tank that takes more than 90 seconds to refill after a flush, visible mineral scale on the valve body, or water that fills to an incorrect level. A running toilet that a new flapper does not fix almost always points to a fill valve that needs replacement.

Fill valve lifespan varies with water quality. In areas with hard water (above 120 ppm dissolved solids), mineral deposits accumulate inside the valve's diaphragm seat and restrict flow within five to seven years. In soft-water areas, a quality fill valve may last 10 to 15 years without any issue. Chloramine-treated water (now used in many municipalities instead of chlorine) can degrade the rubber seals inside older fill valves faster than chlorine alone, so toilets installed before 2010 that have never had a fill valve replacement are overdue for inspection.

A simple dye test confirms whether your fill valve is leaking into the overflow tube. Place a few drops of food coloring in the tank and wait 10 minutes without flushing. If the bowl water picks up color, water is seeping continuously, and the fill valve is either overfilling or there is a flapper leak. If the tank level is above the overflow tube, the fill valve needs adjustment or replacement.

Are there fill valves specifically designed for quiet operation?

Yes. Korky's QuietFILL Platinum (models 528MP and 528GT) and Fluidmaster's 400AH with its wide-angle fill nozzle are both specifically engineered to reduce the sound of water entering the tank. The fundamental noise mechanism is turbulence at the point where pressurized supply water enters the tank. Valves that direct this flow downward through a fill tube into the bowl refill port rather than spraying it directly into standing tank water dramatically reduce the gurgling and splashing sound.

Toilet fill noise is most noticeable in bathrooms adjacent to bedrooms or in open-plan homes. Beyond choosing a quieter valve, routing the fill tube so it deposits water at the bottom of the tank rather than at the waterline reduces turbulence. Most modern fill valves include a refill tube clip and a short overflow tube direction fitting that handles this automatically. If fill noise persists after installing a quiet-rated valve, check whether the refill tube is inserted correctly into the overflow tube and whether water supply pressure is unusually high (above 80 PSI), which amplifies noise in any valve.

Top Toilet Fill Valves Compared (2026)

Model	Type	Shank Range	Flow Rate	Best For	Notable Feature
Fluidmaster 400AH	Float-Cup	7.5–13 in	~3.0 GPM	Most toilets	Anti-siphon, adjustable height
Korky 528MP QuietFILL Platinum	Float-Cup	7–12 in	~2.8 GPM	Noise-sensitive installs	Tower noise dampening
Fluidmaster PRO45	Float-Cup	9–14 in	~3.2 GPM	Tall tanks, professional use	Dual-flow adjustment
Korky 400BK	Float-Cup	7–11 in	~2.5 GPM	Budget replacement	Universal fit, low profile
Fluidmaster 400LS	Floatless	Fixed 9 in	~2.0 GPM	Low-clearance tanks	No visible float mechanism
Fluidmaster 400CRP14	Float-Cup Kit	7.5–13 in	~3.0 GPM	Complete valve + flapper kit	Includes PerforMAX flapper
Korky 528GT QuietFILL	Float-Cup	7–12 in	~2.8 GPM	TOTO-compatible installs	Gray tower, wide valve seat
American Standard 7301111	Float-Cup OEM	Proprietary	~2.2 GPM	Champion 4, Cadet 3	OEM matched fit

Top Fill Valve Picks for 2026

Best Overall

Fluidmaster 400AH Anti-Siphon Fill Valve

4.7 Best For: Universal replacement in any standard gravity-flush toilet

The Fluidmaster 400AH remains the most widely installed aftermarket fill valve on the market, and consistent owner feedback confirms it earns that position through straightforward installation, reliable water level control, and a fill rate that keeps tanks ready fast.

Valve TypeFloat-Cup

Shank Length7.5 to 13 in (adjustable)

Flow Rate~3.0 GPM

Anti-SiphonYes (code compliant)

Warranty5 years (Fluidmaster)

Pros

Fits virtually all 2-inch shank gravity-flush tanks
Easy clip-style water level adjustment
Fast fill rate reduces wait between flushes
Anti-siphon meets all current codes
Widely available for same-day purchase

Cons

Moderately audible water entry (not the quietest valve)
Clip-lock can slip if not seated firmly

The 400AH improved on the original 400A primarily through an adjustable height collar that makes it fit shallow tank lids in modern compact toilets. The clip-style float adjustment is easy to operate -- pinching the clips while sliding the float body up or down sets the water level precisely. Fluidmaster publishes an installation video and detailed instructions, and the process requires nothing beyond a pair of pliers for the supply line nut.

Owner reviews consistently note that it cures the ghost flushing and hissing problems that prompted the repair, and that it holds calibration reliably for years. The 5-year manufacturer warranty is among the longest offered for a fill valve at this price tier.

Expert Take

For a homeowner replacing a failed fill valve without a preference for a specific brand, the Fluidmaster 400AH is the safe, well-supported, code-compliant choice. It is the default recommendation from most licensed plumbers for standard residential toilet repairs.

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Bottom Line: The 400AH is the benchmark aftermarket fill valve -- affordable, reliable, and compatible with more toilet models than any competitor.

Best for Quiet Operation

Korky 528MP QuietFILL Platinum Fill Valve

4.6 Best For: Bedrooms, nurseries, or bathrooms where tank noise is a concern

Korky's QuietFILL Platinum uses a patented tower enclosure that channels incoming water through a submerged path, dramatically reducing the gurgling and splashing noise that standard float-cup valves produce during tank refill.

Valve TypeFloat-Cup (enclosed tower)

Shank Length7 to 12 in (adjustable)

Flow Rate~2.8 GPM

Anti-SiphonYes

Warranty5 years (Korky)

Pros

Significantly quieter than standard float-cup valves
Screw-type water level adjustment holds precisely
American-made by Lavelle Industries
Compatible with most one-piece and two-piece tanks

Cons

Slightly bulkier tower can be tight in narrow tanks
Screw adjustment requires a screwdriver rather than tool-free clip

Korky manufactures all its fill valves and flappers in Burlington, Wisconsin -- a selling point for buyers who prefer American-made parts. The 528MP's screw-top adjustment mechanism offers finer calibration than a clip-slide system and holds the water level accurately once set. Owner reviews rate it particularly well by users replacing noisy valves in guest bathrooms and master bedroom bathrooms where middle-of-the-night flushing sound is a real household issue.

The one area where the Korky 528MP yields to the Fluidmaster 400AH is tank clearance. The tower enclosure adds about a half-inch to the overall footprint, and in a few ultra-compact one-piece toilet tanks it may be a tight fit. Checking inside tank dimensions before ordering avoids the rare compatibility issue.

Expert Take

If noise is the primary complaint about a running or recently repaired toilet, the Korky QuietFILL Platinum addresses the root cause rather than just replacing like-for-like. Its noise reduction is genuine and owner-verified, not a marketing claim.

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Bottom Line: The QuietFILL Platinum is the right valve when noise reduction matters as much as reliable fill performance.

Best for Tall Tanks

Fluidmaster PRO45 ProFill Fill Valve

4.5 Best For: Older two-piece toilets with deep tanks; professional installations

The Fluidmaster PRO45 extends shank range to 9 to 14 inches and adds a dual-flow adjustment that allows finer tuning of both fill rate and water level independently, making it the preferred valve for professional plumbers replacing parts in older high-tank gravity systems.

Valve TypeFloat-Cup

Shank Length9 to 14 in (adjustable)

Flow Rate~3.2 GPM

Anti-SiphonYes

Warranty5 years (Fluidmaster)

Pros

Extended shank covers deep older toilet tanks
Highest flow rate of the standard float-cup class
Dual-flow adjustment for precision setup
Professional-grade build quality

Cons

Over-specified for shallow modern tanks
Costs more than the 400AH without added benefit for typical installs

Deep tanks are common in older American Standard and Kohler two-piece toilets manufactured before 1994. These tanks can measure 13 to 14 inches from the floor to the water line, and a standard 400AH at 13 inches maximum shank length is borderline. The PRO45's 14-inch maximum provides the necessary clearance and ensures the float operates within the correct portion of the tank. The higher-rated flow of 3.2 GPM also makes it a good choice in commercial or high-traffic residential settings where fast tank recovery is valued.

Expert Take

The PRO45 is the right choice when the standard 400AH measures just short of fitting properly. Its extended shank solves a specific problem that adding adapters or attempting to force a shorter valve never solves cleanly.

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Bottom Line: The PRO45 is purpose-built for deep tanks and professional installations where the standard 400AH falls short.

Best Complete Kit

Fluidmaster 400CRP14 Fill Valve and Flapper Repair Kit

4.6 Best For: Homeowners who want to replace both internal tank parts in one repair

Replacing just the fill valve while leaving an aged flapper in place often means a second repair within a year. Fluidmaster's 400CRP14 bundles the proven 400-series fill valve with a PerforMAX adjustable flapper, addressing both of the most common causes of a running toilet in a single purchase.

ContentsFill valve + PerforMAX flapper

Shank Length7.5 to 13 in

Flapper Compatibility2-inch flush valve seats

Anti-SiphonYes

Warranty5 years

Pros

Addresses both fill valve and flapper in one service call
PerforMAX flapper is adjustable for water-saving or power-flush configurations
Cost-effective versus buying parts separately

Cons

Flapper only fits 2-inch seats, not 3-inch or 4-inch flush valves
Not ideal for TOTO or Kohler toilets that use proprietary flapper designs

The PerforMAX flapper included in this kit offers a rare adjustable water-per-flush feature. Sliding the adjustment ring controls how much water exits the tank before the flapper closes, which can optimize flush performance in toilets where the factory flapper timing is slightly off. This is particularly useful in American Standard Champion 4 and Cadet 3 toilets where third-party flappers sometimes cause double-flushing or weak flushes due to mismatched close timing.

Expert Take

When one tank component fails on a toilet that is several years old, the other primary component is usually near end of life too. Replacing both at once with matched Fluidmaster parts is simply more efficient than making two trips to the hardware store six months apart.

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Bottom Line: The smartest single-purchase fix for any running or ghost-flushing toilet that has never had its internal parts replaced.

Best for Low-Profile Tanks

Fluidmaster 400LS Floatless Fill Valve

4.3 Best For: Space-constrained tanks where a float cup physically cannot operate

The 400LS uses a pressure-sensing diaphragm at the base rather than a float cup, making it ideal for one-piece toilets with very shallow tank lids where a standard float-cup valve would contact the lid and prevent proper water level operation.

Valve TypeFloatless / Pressure-Sensing

HeightFixed 9 in (no adjustment)

Flow Rate~2.0 GPM

Anti-SiphonYes

Warranty3 years

Pros

No float mechanism to contact shallow tank lids
Clean, uncluttered tank appearance
Works in tanks too shallow for adjustable float valves

Cons

Lower flow rate than float-cup alternatives
Fixed height limits compatibility with deep tanks
Pressure sensing can be sensitive to supply water pressure swings

Floatless fill valves are a niche product, but they solve a real problem in specific toilet designs. Compact one-piece toilets from Swiss Madison, Woodbridge, and some Kohler lines occasionally have such shallow tanks that a standard float cup either contacts the lid at rest or cannot travel freely to shut off at the correct water level. The 400LS resolves this by eliminating the float entirely. Water level is controlled by the pressure setpoint, which adjusts via a dial at the base of the unit.

Expert Take

The 400LS is not a universal replacement choice, but for the specific situation it addresses, there is no better solution. If the installed float-cup valve is touching the tank lid when the tank is full, a floatless valve is the correct fix.

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Bottom Line: A specialized but important option for shallow-tank toilets where standard float-cup valves simply will not fit.

What is the correct way to install a toilet fill valve?

Installing a fill valve requires turning off the water supply at the shut-off valve, flushing to empty the tank, disconnecting the supply line, unthreading and removing the old valve, inserting the new valve through the tank opening and hand-tightening the locknut from below, reconnecting the supply line, adjusting the water level to 1 inch below the top of the overflow tube, and then slowly reopening the water supply. The entire process takes approximately 10 to 20 minutes for most homeowners and requires no specialized tools beyond basic pliers.

Step-by-step, a fill valve replacement follows this sequence. First, turn the shut-off valve behind the toilet clockwise until it stops. Flush the toilet to drain the tank, then hold the flush lever down to remove as much water as possible. Place towels on the floor around the base of the toilet in case of drips. Disconnect the supply line from the bottom of the tank using an adjustable wrench or channel-lock pliers. Look into the tank: you will see the fill valve near the left side of the tank with a locknut holding it against the tank floor.

Reach into the tank to hold the valve body steady while you unthread the locknut from below with pliers. Some valves require simultaneously pressing and turning the top cap to release the valve before the locknut comes off. Once the locknut is free, lift the old valve out of the tank and discard it along with any old gaskets.

Insert the new valve through the tank hole. Nearly all modern fill valves use the same 7/8-inch tank hole standard. Thread the new locknut onto the valve shank from below and hand-tighten, then snug it with pliers. Do not overtighten or the plastic shank can crack. Adjust the height of the valve body before tightening -- the critical height relationship is that the critical level mark (labeled "CL" on most valves) must sit at least 1 inch above the top of the overflow tube. Set the water level at the same time by adjusting the float position.

Reconnect the supply line and slowly open the shut-off valve. Watch the tank fill and confirm water stops at the correct level, which should be approximately 1 inch below the top of the overflow tube. Check under the tank for any drips at the locknut, and tighten slightly if needed. Route the refill tube into the top of the overflow tube. The job is complete.

For more detailed instructions, see our companion article on how to replace a toilet fill valve.

How does a fill valve affect water efficiency and EPA WaterSense compliance?

The fill valve does not directly determine gallons per flush -- that is set by the tank volume and flush valve. However, a malfunctioning or poorly calibrated fill valve can waste enormous amounts of water through phantom leaks. EPA WaterSense research estimates that a continuously running toilet wastes an average of 200 gallons per day. A properly functioning fill valve that holds the water level 1 inch below the overflow tube eliminates this waste. WaterSense-certified toilets rely on the fill valve being correctly set to deliver the certified 1.28 GPF or 1.0 GPF per flush.

Water efficiency in toilets is measured at the toilet level, not at individual component level. The EPA WaterSense program certifies complete toilets, including the TOTO Drake II (1.28 GPF), the Kohler Cimarron (1.28 GPF), the American Standard Cadet 3 (1.28 GPF), and the Woodbridge T-0001 (1.28 GPF dual flush), among hundreds of others. These certifications assume that the fill valve is working correctly and calibrated to the design water level.

When a fill valve overfills the tank past the design water level, each flush uses more water than the certified GPF rating. Conversely, a fill valve adjusted too low results in incomplete flushes that require double-flushing, negating the water-saving benefit. Correct fill valve calibration is therefore a genuine water conservation action, not just a repair task.

The relationship between fill valve health and household water bills is straightforward. In a household with three bathrooms, each with a mildly running toilet that wastes 30 gallons per day, the annual wasted water totals more than 32,000 gallons. At typical residential water rates, this adds measurably to annual utility costs. Replacing all three fill valves eliminates this waste with less than an hour of total labor. See our guide to best flushing toilets for a full breakdown of how flush systems and water efficiency interact.

For households specifically pursuing water conservation, it is also worth verifying whether the toilet qualifies for a utility rebate. Many water utilities across the Southwest, California, Texas, and Florida offer rebates of $25 to $150 for replacing pre-1.6 GPF toilets with EPA WaterSense-certified models. A repair rather than replacement may not qualify for rebates, but it does keep existing efficient toilets performing at their certified specification.

Frequently Asked Questions

Are all toilet fill valves universal?

Most modern fill valves fit any gravity-flush toilet with a standard 7/8-inch tank opening. However, pressure-assist toilets use proprietary sealed fill systems and require brand-specific parts. Very shallow one-piece tanks may also need low-profile or floatless valves. Always measure tank depth and check whether your toilet uses gravity or pressure-assist flushing before ordering.

How long does a toilet fill valve last?

A quality fill valve from Fluidmaster or Korky typically lasts 5 to 15 years, depending on water quality. Hard water with high mineral content (above 120 ppm) accelerates wear on the valve seat and diaphragm, shortening lifespan to the 5 to 7 year range. Soft water installs can see a fill valve last 15 years with no problems.

Can I replace a fill valve without turning off the main water supply?

You need to close the shut-off valve located on the supply line behind the toilet, not the main house supply. Most toilets have a quarter-turn or multi-turn shut-off valve at the wall. If this valve does not close fully due to age or corrosion, you may need to close the main water supply temporarily. See our guide on toilet shut-off valve replacement if the valve itself is faulty.

Why does my toilet still run after replacing the fill valve?

If the toilet continues to run after a new fill valve is installed, the flapper is the next component to check. A worn or poorly seated flapper allows water to seep into the bowl continuously, causing the fill valve to cycle repeatedly to maintain tank level. Use the food coloring dye test: drop dye in the tank and wait 10 minutes; if color appears in the bowl without flushing, replace the flapper.

What is the difference between a fill valve and a flush valve?

The fill valve (also called a ballcock or inlet valve) controls water flowing INTO the tank from the supply line. The flush valve is the opening at the tank floor, sealed by the flapper, that releases water DOWN into the bowl when you flush. These are separate components with separate failure modes. A running toilet most commonly points to one or both of these valves needing replacement.

Do fill valves affect flush strength?

Indirectly, yes. The fill valve determines the water level in the tank, and water level affects the hydraulic pressure available at the start of each flush. If the fill valve is calibrated too low, the toilet starts each flush with less water and less head pressure, which can result in weak flushes, especially in MaP-tested toilets where the certified score depends on the designed fill volume.

Is there a fill valve specifically for TOTO toilets?

TOTO sells OEM replacement fill valves for its Drake, Drake II, UltraMax II, and Aquia IV toilet families. These are the safest choice for maintaining original performance and water level calibration. The Korky 528GT QuietFILL is widely reported by owners to be a compatible aftermarket option for most TOTO two-piece tanks, but confirming tank dimensions against the valve's shank range before purchasing is advisable.

What causes a fill valve to hiss or whistle?

Hissing or whistling during tank fill usually indicates mineral buildup inside the valve seat restricting flow, a worn diaphragm seal, or a partially closed shut-off valve that creates turbulent flow. Cleaning debris from the valve cap diaphragm (twist the cap, remove, and rinse) sometimes resolves the issue temporarily, but a valve that hisses persistently is near end of life and should be replaced.

Can a fill valve cause ghost flushing?

Ghost flushing (the toilet cycling on by itself without being flushed) is almost always caused by water slowly draining out of the tank. The fill valve cycles to refill the tank after water drops below the trigger point. The water is leaving through a leaking flapper, not through the fill valve itself. However, a fill valve set too high will continually overflow into the overflow tube, which looks like a running toilet and can cause the same symptom.

How do I adjust the water level on a float-cup fill valve?

On Fluidmaster float-cup valves, pinch the spring clip on the float cup while sliding the cup up (higher water level) or down (lower water level) on the shaft, then release. On Korky valves, turn the adjustment screw clockwise to lower the water level or counterclockwise to raise it. The target level is 1 inch below the top of the overflow tube, which ensures efficient flush volume without wasting water through overflow. A detailed walkthrough is in our water level adjustment guide.

What is the "critical level" mark on a fill valve?

The critical level (labeled "CL") is an embossed marking on the valve body that must sit at least 1 inch above the top of the overflow tube when the valve is installed. This ensures the anti-siphon protection remains functional. If the CL mark is below the overflow tube top, the valve is installed at the wrong height and the anti-siphon feature cannot work correctly. Adjust the valve height before finalizing installation.

Can I install a 1.28 GPF fill valve to make my toilet more water efficient?

No -- the fill valve does not control gallons per flush. GPF is determined by tank volume and flush valve design. Modifying the fill valve calibration to add less water per cycle risks under-flushing and increased clog risk. Water-efficient flushing requires an EPA WaterSense-certified toilet with the correct volume and bowl design. The fill valve's role is to accurately deliver whatever water volume the tank is designed to hold, not to change it.

What tools do I need to replace a fill valve?

The basic toolkit is an adjustable wrench or 10-inch channel-lock pliers for the supply line coupling nut and the fill valve locknut, a bucket or towels for residual water, and the new fill valve with its included hardware. No cutting, soldering, or specialized plumbing tools are required. The entire job is within reach of any homeowner comfortable with basic home maintenance.

How tight should the fill valve locknut be?

Hand-tight plus approximately one-quarter to one-half turn with pliers is the correct specification. Overtightening the plastic locknut can crack the shank or the tank floor. If the installation leaks at the locknut after being tightened to this specification, the problem is usually a missing or misaligned rubber gasket at the shank base, not insufficient torque.

Does water pressure affect fill valve performance?

Yes. Most fill valves are rated to operate within a supply pressure range of approximately 10 to 80 PSI. Very high pressure (above 80 PSI) can shorten valve lifespan and increase hissing noise. Very low pressure (below 20 PSI) can result in slow fill times. If your household water pressure is outside this range, installing a pressure-reducing valve at the main supply line before the toilet shut-off addresses the issue at the source.

Is it worth buying an OEM fill valve versus aftermarket?

For most standard toilets, the Fluidmaster 400AH or Korky QuietFILL Platinum is a fully adequate replacement for OEM valves from American Standard, Kohler, Gerber, and Woodbridge. For TOTO toilets, where tank geometry and overflow tube height are more critical to correct water level, TOTO OEM parts or carefully confirmed aftermarket models are preferred. For pressure-assist systems, only OEM or manufacturer-specified parts are acceptable.

How do I know what size fill valve to buy for my toilet?

Measure the inside depth of your tank from the bottom (where the valve sits) to the underside of the tank lid. Then measure the existing valve's height. Choose a replacement valve with an adjustable shank range that covers your measurement. For most residential two-piece toilets, a valve adjustable from 7 to 13 inches covers the range. For unusually shallow or deep tanks, measure first and select accordingly.

Can I use a fill valve designed for a 1.6 GPF toilet in a 1.28 GPF toilet?

Yes. The fill valve itself is not GPF-specific. What matters is that you calibrate the water level correctly for your specific tank's design fill line, which is marked on most modern tanks as a waterline or indicated by the overflow tube height. As long as the valve's shank length is compatible and the float is set to fill to the correct level, any quality fill valve works in any gravity-flush tank.

What is a dual-flush fill valve?

Some manufacturers describe fill valves bundled with dual-flush mechanisms as dual-flush fill valves, but technically the fill valve itself does not control whether the toilet is single or dual flush. The dual-flush mechanism is part of the flush valve and actuator assembly. The fill valve in a dual-flush toilet still functions the same way as in any other gravity-flush toilet -- it refills the tank to the design water level after each flush, regardless of which flush mode was used.

How do I stop my new fill valve from making a loud noise when filling?

First, confirm the refill tube is routed into the overflow tube rather than loose inside the tank. A refill tube that dumps water onto the tank floor creates noise. Second, confirm the shut-off valve is fully open -- a partially open shut-off creates turbulent flow that amplifies fill sound. If noise persists, consider switching to a Korky QuietFILL model, which is specifically engineered to minimize fill sound through its enclosed tower design.

Sources

EPA WaterSense, epa.gov/watersense
MaP flush testing, map-testing.com
Manufacturer published specifications
Fluidmaster product documentation and installation guides, fluidmaster.com
Korky product specifications and installation resources, korky.com
TOTO USA specification sheets, totousa.com
American Standard published product data, americanstandard-us.com
Kohler published product specifications, kohler.com

Our Verdict

For the overwhelming majority of gravity-flush toilets, the Fluidmaster 400AH is the right fill valve to buy in 2026. It fits more tanks than any alternative, installs without specialized tools, delivers a fast fill rate, and carries a 5-year warranty at a price that makes deferred repair decisions hard to justify. If noise is the primary issue, upgrade to the Korky 528MP QuietFILL Platinum. If your tank is unusually deep, the Fluidmaster PRO45 covers the full range. No matter which model you choose from this guide, a quality fill valve replacement resolves nearly every common running toilet complaint and pays for itself quickly through eliminated water waste.

Related Guides

How we rank & our data sources

We do not run physical lab tests. Rankings are built from published, verifiable data and real owner feedback, never paid placement.

MaP (Maximum Performance) flush scores
EPA WaterSense certification & GPF ratings
Manufacturer specifications (trapway size, flush-valve, rough-in)
Verified owner reviews from Amazon, Home Depot & Lowe’s

Researched by Marcus Bell · Last updated June 28, 2026 · Our review method

Researched by Marcus Bell

Marcus compiles bathroom-fixture data, MaP flush scores, GPF ratings, trapway and flush-valve specs, and weighs them against thousands of verified owner reviews to build our rankings. He does not run physical lab tests; every verdict is sourced from published specifications, certifications (MaP, EPA WaterSense) and real owner feedback.

Updated June 2026 · Buying Guides

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