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Best Toilet Fill Valve in 2026 — Fluidmaster 400H vs Korky QuietFILL, the Critical Level Mark, and Why a Valve That Will Not Shut Off Ends Up on the Floor

Best Toilet Fill Valve in 2026

Fluidmaster 400H vs Korky QuietFILL, the Critical Level Mark, and Why a Valve That Will Not Shut Off Ends Up on the Floor

5 picks compared · prices, ratings and stock checked October 13, 2026

Our Top Pick

For most two-piece toilets, the Fluidmaster 400H Universal Toilet Fill Valve, with separate tank and bowl level dials and a 9 to 14 in height range. For a short or one-piece tank, the Korky 528 QuietFILL Platinum Toilet Fill Valve, which adjusts down to 7.75 in. If the flapper is old too, the Fluidmaster 400A kit replaces both in one order.

4.6 on Amazon · 18,928 ratings

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Quick answer

The best toilet fill valve for most two-piece toilets is the Fluidmaster 400H Universal Toilet Fill Valve, rated 4.6 stars across 18,928 Amazon ratings, because it adjusts from 9 to 14 in tall and has separate dials for the tank level and the bowl refill. If your tank is shorter than 9 in, buy the Korky 528 QuietFILL Platinum Toilet Fill Valve, which goes down to 7.75 in. Whichever valve you fit, set the water line about 1 in below the top of the overflow tube and keep the valve's critical level mark at least 1 in above the tube, as US plumbing codes require.

Our Picks at a Glance

Every pick below is currently stocked — ratings and stock read from Amazon on 13 October 2026.

All picks compared at a glance
PickProductRatingWhere to buy
Best OverallFluidmaster 400H Universal Toilet Fill Valve (Tank and Bowl Dials, 9 to 14 in)4.6★Amazon
Best Kit With FlapperFluidmaster 400A Fill Valve and 2-Inch Flapper Toilet Repair Kit (9 to 14 in, 5-Year Warranty)4.6★Amazon
Best for Short TanksKorky 528 QuietFILL Platinum Toilet Fill Valve (7.75 to 13.5 in, Twist-Lock)4.5★Amazon
Best for Kohler Class Five ToiletsKohler GP1083167 Genuine Part Silent Fill Valve Kit (Class Five Toilets, Black Shank)4.6★Amazon
Best for Flapperless ToiletsFluidmaster 703AP4 Fill Valve for Glacier Bay and Niagara Flapperless Toilets4.7★Amazon

How this page was made: we compare the current Amazon listings, the makers' published specs and what verified buyers report, then rank by fit for the job. Ratings, review counts and stock are read from Amazon and dated. We earn a commission on purchases through our links; it does not change the order. Reviewed by Marcus Reed, IICRC-certified Water Restoration Technician.

Full Reviews

Each pick in detail: what the listing states, what buyers report, and where it falls short.

#1
Best Overall

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Listing verified 13 Oct 2026

Fluidmaster 400H Universal Toilet Fill Valve (Tank and Bowl Dials, 9 to 14 in)See it on Amazon ↗

Best Overall

Fluidmaster 400H Universal Toilet Fill Valve (Tank and Bowl Dials, 9 to 14 in)

4.6(18,928 reviews)

Quick Verdict

Fluidmaster 400H Universal Toilet Fill Valve: tank and bowl dials in a 9 to 14 in valve for most two-piece toilets.

Key Specs

Height range (stated)

9 to 14 in, EZ-Twist adjustment

Adjustment (stated)

Separate tank water level and bowl water level dials

Fit (stated)

Universal for most toilet models and brands

Fixes (stated)

Noisy or slow-filling valves

Shank

Not stated on this listing

Included parts

Not itemized on this listing; step-by-step instructions included

Pros

  • A bowl refill dial as well as a tank dial, so you can stop over-filling the bowl without starving the tank
  • 9 to 14 in height range covers most standard two-piece tanks
  • Fluidmaster's listing says it is built to replace slow-filling valves, the usual complaint on older ballcocks

Cons

  • Does not adjust below 9 in, so a low-profile tank may need the Korky instead
  • The listing does not itemize what is in the box or name the shank material
  • The quietest and most powerful claim is the maker's; no decibel or flow figure is stated

Suited to

Replacing a noisy, slow or non-stopping valve in a standard two-piece toilet

Our take

Two dials are what set the 400H apart from a basic fill valve. The tank dial sets how high the water climbs before the valve shuts, which is where you hold the line about 1 in below the overflow tube. The bowl dial controls how much water the refill tube sends down the overflow tube while the tank fills, and that is the one most people never had: too little and the bowl sits low and smells, too much and gallons go straight down the drain on every flush. The 9 to 14 in range suits most two-piece tanks, but measure from the tank floor to the top of the overflow tube before ordering, because the valve's critical level mark has to end up above that tube. The listing is quiet on what ships in the box, so keep your old refill clip until you see the new one.

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#2
Best Kit With Flapper

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Fluidmaster 400A Fill Valve and 2-Inch Flapper Toilet Repair Kit (9 to 14 in, 5-Year Warranty)See it on Amazon ↗

Best Kit With Flapper

Fluidmaster 400A Fill Valve and 2-Inch Flapper Toilet Repair Kit (9 to 14 in, 5-Year Warranty)

4.6(33,640 reviews)

Quick Verdict

Fluidmaster 400A Fill Valve and 2-Inch Flapper Kit: valve and flapper together for an older 2 in toilet.

Key Specs

Height range (stated)

9 to 14 in

Includes (stated)

400A fill valve and a solid-frame 2 in flapper

Fit (stated)

Most 2 in flush valve toilets

Flapper (stated)

Solid frame, said to resist twisting

Warranty (stated)

5 years

Bowl refill adjustment

Not stated on this listing

Pros

  • Fixes a cracked fill valve and a leaking flapper in one order
  • A 5-year warranty, stated on the listing
  • The same 9 to 14 in range as the 400H
  • The largest buyer record on this page

Cons

  • The included flapper is 2 in only; a 3 in flush valve needs a different kit
  • No bowl refill dial is mentioned, unlike the 400H
  • If your flapper is fine, you are buying a part you will not use

Suited to

A toilet that both runs and refills slowly, where the flapper and fill valve are the same age

Our take

When a toilet runs, the dye test tells you whether the flapper is leaking, but it says nothing about the fill valve, and on a toilet that is ten or fifteen years old both parts are usually tired. This kit replaces the pair. The 400A is the plain version of the Fluidmaster valve, with the tank level adjustment and the 9 to 14 in height range but without the separate bowl refill dial the 400H carries, which is why it sits second. The flapper is Fluidmaster's solid-frame 2 in type, and the listing is clear that it fits 2 in flush valves, so measure the opening first; a 3 in toilet needs Fluidmaster's 3 in kit instead. The 5-year warranty covers both parts. This is not the kit for a newer high-efficiency bowl with the larger valve.

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#3
Best for Short Tanks

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Korky 528 QuietFILL Platinum Toilet Fill Valve (7.75 to 13.5 in, Twist-Lock)See it on Amazon ↗

Best for Short Tanks

Korky 528 QuietFILL Platinum Toilet Fill Valve (7.75 to 13.5 in, Twist-Lock)

4.5(6,833 reviews)

Quick Verdict

Korky 528 QuietFILL Platinum Toilet Fill Valve: a 7.75 in minimum and a fully itemized kit for short tanks.

Key Specs

Height range (stated)

7.75 to 13.5 in, twist-lock adjustment

Fit (stated)

Two-piece and one-piece toilets; replaces ballcocks and worn valves

Included (stated)

Fill valve, refill tube, metal refill tube clip, mounting nut, cone washer, refill adjuster, coupling nut, tamper-proof key and instructions

Install time (stated)

Less than 5 minutes

Material (stated)

Korky's chlorazone red rubber for the sealing parts

Made in

USA (Wisconsin), per the listing

Pros

  • Adjusts down to 7.75 in, the lowest minimum on this page, for low-profile and older tanks
  • The listing itemizes every part in the box, including a metal refill clip and a refill adjuster
  • Named for one-piece as well as two-piece toilets
  • Made in the USA, per the listing

Cons

  • Tops out at 13.5 in, half an inch below the Fluidmaster range
  • No warranty term on the listing
  • The tamper-proof key has to be kept somewhere, or you cannot re-adjust the valve later

Suited to

A low-profile, one-piece or older tank where a 9 in minimum valve sits too tall

Our take

Height is the spec that decides whether a fill valve can be installed at all. The valve has to be short enough to clear the tank lid and tall enough to put its critical level mark above the overflow tube, and some one-piece and older tanks leave less than 9 in to work with. Korky's 528 adjusts from 7.75 in, which is why it is the pick for those tanks. The listing is the most complete on this page: it names the refill tube, a metal clip for it, the cone washer and coupling nut, and a refill adjuster that does the job of Fluidmaster's bowl dial. The sealing parts are Korky's chlorazone red rubber. Measure from the tank floor to the top of the overflow tube, add 1 in for the mark, and check the lid still closes at that height.

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#4
Best for Kohler Class Five Toilets

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Listing verified 13 Oct 2026

Kohler GP1083167 Genuine Part Silent Fill Valve Kit (Class Five Toilets, Black Shank)See it on Amazon ↗

Best for Kohler Class Five Toilets

Kohler GP1083167 Genuine Part Silent Fill Valve Kit (Class Five Toilets, Black Shank)

4.6(10,175 reviews)

Quick Verdict

Kohler GP1083167 Silent Fill Valve Kit: the matching part for Class Five toilets, chosen by shank color.

Key Specs

Fits (stated)

All Kohler Class Five toilets

Shank check (stated)

A black shank takes this part; a grey shank takes Kohler GP1138930

Valve type (stated)

Manual, adjustable

Dimensions (stated)

12.5 in x 3.5 in x 3 in

Warranty note (stated)

Kohler says to use genuine parts to protect the toilet's warranty

Height range

Not stated on this listing

Pros

  • The maker's own part for Class Five toilets, with a stated shank-color check to confirm fit
  • Keeps a Kohler toilet warranty intact, per Kohler's listing
  • Adjustable, per the listing

Cons

  • Only for Kohler Class Five toilets; it is not a universal valve
  • The listing gives no height range, so you cannot compare it to the Fluidmaster or Korky figures
  • Two near-identical Kohler parts exist, and ordering the wrong shank color means a return

Suited to

A Kohler Class Five toilet still under warranty, or one where a universal valve did not sit right

Our take

Universal valves fit most toilets, but a maker's own part is the safer buy when the toilet is under warranty or when its tank is shaped around a specific valve. Kohler's Class Five flush uses a large flush valve and a tank that fills quickly, and Kohler sells this valve as the matching fill part. The useful detail on the listing is the shank check: look at the color of the threaded shank on your old valve, black takes this part and grey takes GP1138930. Do that before ordering, because the two look alike in photos. What the listing does not give is a height range or an itemized parts list, so there is no way to compare it with the Fluidmaster or Korky figures on this page. If your toilet is not a Kohler Class Five, skip this and buy a universal valve.

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#5
Best for Flapperless Toilets

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Fluidmaster 703AP4 Fill Valve for Glacier Bay and Niagara Flapperless ToiletsSee it on Amazon ↗

Best for Flapperless Toilets

Fluidmaster 703AP4 Fill Valve for Glacier Bay and Niagara Flapperless Toilets

4.7(6,218 reviews)

Quick Verdict

Fluidmaster 703AP4 Fill Valve: the dedicated replacement for Glacier Bay and Niagara flapperless toilets.

Key Specs

Fits (stated)

Glacier Bay and Niagara flapperless toilets, as a direct replacement

Purpose (stated)

Restores refill speed on those toilets

Instructions

Included, per the listing

Height range

Not stated on this listing

Adjustment

Not stated on this listing

Warranty

Not stated on this listing

Pros

  • A direct replacement for a toilet type that universal valves are not sold for
  • Fluidmaster names the slow refill these toilets develop as the problem it fixes
  • The highest buyer rating on this page

Cons

  • No use on an ordinary flapper toilet
  • No height range, dial or parts list on the listing
  • You must know whether your toilet is a flapperless model, which the tank lid does not always say

Suited to

A Glacier Bay or Niagara flapperless toilet that has started filling slowly

Our take

Flapperless toilets from Glacier Bay and Niagara do not have a flapper at all. A bucket inside the tank tips to dump water into the bowl, and the fill valve refills that bucket. A universal valve from the other picks on this page is not sold for that layout, which is why Fluidmaster makes this dedicated part. The listing is short on specifics: it says the valve is a direct replacement and restores refill speed, and nothing about height or adjustment. Lift your tank lid before you order. If you see a tipping bucket rather than a flapper on a hinge, this is the valve; if you see a flapper, buy the 400H or the Korky. For any tank that has started to refill slowly, also check that the supply shutoff is fully open and the inlet screen is clear before replacing anything.

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Buyer's Guide

What to know before you buy.

How a Fill Valve Fails, and Where the Water Goes

A fill valve has one job: open when the tank empties, close when it is full. It fails in two directions. A valve that stops short gives a weak flush and a low bowl. A valve that will not shut off is the one that costs money. Water climbs past the set level, reaches the top of the overflow tube and runs down it into the bowl and away, all day, with no puddle and no sound beyond a faint hiss. The overflow tube is the safety outlet. If it is blocked, the water keeps climbing and comes over the rim of the tank onto the floor, and that water finds the subfloor and the ceiling below. EPA says water-damaged areas should be dried within 24 to 48 hours to prevent mold growth, so a tank that has overflowed is not only a plumbing job.

The Critical Level Mark and the 1 in Water Line

Every fill valve sold for US toilets carries a critical level mark, usually printed CL on the valve body. US plumbing codes require that mark to sit at least 1 in above the top of the overflow tube. The reason is backflow: if street pressure drops while the tank is full, a valve inlet sitting below the water line could siphon tank water back into the supply pipes, and the CL mark keeps the inlet above any water that could do that. That is why height adjustment matters more than it looks. Set the valve so the CL mark clears the overflow tube by 1 in, then set the water level itself about 1 in below the top of the tube, so a slow drift upward still has somewhere to go before it reaches the overflow. The refill tube clips to the top of the overflow tube and must not be pushed down inside it, or it siphons the tank between flushes and the toilet runs.

Height Range, Dials and What Comes in the Box

Measure before you buy. Stand a tape on the floor of the tank and read the height of the overflow tube, then add 1 in for the critical level mark; the valve has to reach that height and still clear the lid. Fluidmaster's 400H and 400A adjust from 9 to 14 in, Korky's 528 from 7.75 to 13.5 in, and the Kohler and Glacier Bay parts state no range at all. Dials are the second check. A tank dial sets the water line; a bowl or refill adjuster sets how much water goes down the overflow tube to refill the bowl, which is the setting that stops a bowl sitting low or wasting water. The 400H has both, and the Korky 528 includes a refill adjuster. Finally, read the parts list. Korky itemizes the refill tube, metal clip, cone washer, coupling nut and key; the 400H listing does not, so keep your old parts until the box is open.

Which Fill Valve Fits Which Toilet

A universal valve threads through the same hole in the tank floor on most two-piece toilets, so Fluidmaster and Korky fit the bulk of American Standard, TOTO, Gerber, Mansfield and Kohler tanks. The exceptions are toilets built around their own valve. Kohler Class Five toilets have a Kohler part, chosen by the color of the old valve's shank, black or grey. Glacier Bay and Niagara flapperless toilets refill a tipping bucket rather than a flapper tank and take Fluidmaster's 703AP4. One-piece toilets are the other case: the tank is low and the lid clearance tight, which is where the Korky 528's 7.75 in minimum earns its place. A tank fed from the side rather than through the floor needs a valve made for it, and none of the picks on this page is. If your old valve is a brass ballcock with a float ball on an arm, any of the universal picks replaces it; the arm and ball are not reused.

Who Should Not Buy a Fill Valve, and When to Call a Plumber

A new fill valve is the wrong purchase when the dye test shows color in the bowl: that is the flapper, and the fill valve is only running because the tank keeps losing water. It is also the wrong purchase for a toilet that leaks at the base or sweats on the outside of the tank. Replacing a valve is a half-hour job with the supply shut off and the tank emptied, and most people can do it. Call a licensed plumber when the supply shutoff under the toilet will not close or weeps when you turn it, when the old valve's shank nut is seized and the tank is thin porcelain, or when the tank has already overflowed onto the floor more than once, because the floor under it needs checking. HearthDry's phone line reaches water damage restoration companies for a soaked floor or ceiling; it is not a plumber's line.

After the Swap: The Settings That Stop a Second Call

Turn the supply back on slowly and let the tank fill. Check three things. First, the water line should rest about 1 in below the top of the overflow tube; adjust the tank dial or float until it does. Second, the refill tube should clip to the rim of the overflow tube with its end above the water, not pushed down into it. Third, the bowl should refill to its normal level and stop; if it keeps trickling or sits low, turn the bowl refill adjuster. Then listen. A valve that cycles on for a few seconds every half hour without anyone flushing means the tank is losing water, which sends you back to the flapper. Run EPA's dye test a day later to be sure, and wipe the floor behind the toilet dry so any new drip from the supply coupling shows up.

Frequently Asked Questions

How do I know if my toilet fill valve is bad?

Four signs: the tank keeps running or hisses after it should have stopped, it fills slowly, the bowl sits low after a flush, or the tank refills on its own even though the dye test shows no color in the bowl.

That last check matters, because a leaking flapper makes a fill valve run too. Reach into the tank and lift the float by hand; if the water does not stop, the valve is done.

Are toilet fill valves universal?

Mostly, for two-piece toilets with the supply entering through the tank floor. Fluidmaster's 400H and Korky's 528 are both listed as universal and fit the bulk of American Standard, TOTO, Gerber, Mansfield and Kohler tanks.

The exceptions are Kohler Class Five toilets, which have their own Kohler part, Glacier Bay and Niagara flapperless toilets, which take Fluidmaster's 703AP4, side-fed tanks, and very low one-piece tanks that need a valve adjusting below 9 in.

How high should the water level be in a toilet tank?

About 1 in below the top of the overflow tube. Higher than that and water spills down the tube and the valve never shuts off; much lower and the flush weakens.

The valve's critical level mark, printed CL on the body, is a separate height and must sit at least 1 in above the overflow tube, which US plumbing codes require to stop tank water siphoning back into the supply.

Why does my toilet fill valve keep running?

Either the valve cannot close or the tank keeps emptying. If the water line is at or above the overflow tube, the float or dial is set too high; turn it down.

If the line is right and the valve still runs, grit under its seal or a worn diaphragm is holding it open, and a new valve is the fix. If the valve cycles on and off by itself, the tank is losing water past the flapper, and a dye test will show color in the bowl.

Can I replace a toilet fill valve myself?

Usually, yes. Shut off the supply, flush and sponge out the tank, unscrew the supply coupling and the shank nut under the tank, lift the old valve out and fit the new one with its CL mark 1 in above the overflow tube.

The jobs to hand to a licensed plumber are a shutoff valve that will not close or weeps, a seized shank nut on an old tank, or a toilet that has already flooded the floor, because then the floor needs checking too.

Is Fluidmaster or Korky better for a toilet fill valve?

It dependsOn the tank. Fluidmaster's 400H has separate tank and bowl dials and adjusts from 9 to 14 in, which suits most two-piece toilets.

Korky's 528 adjusts from 7.75 to 13.5 in, lists every part in the box, and is named for one-piece toilets as well, which makes it the pick for a short tank. Measure from the tank floor to the top of the overflow tube and let that number decide.

Who do I call right now for water damage?

Call (888) 840-6512. The line is answered 24 hours a day, seven days a week, and connects you with an IICRC-certified water damage restoration company that serves your area. A recorded menu picks up first: choose water damage or mold, key in your 5-digit ZIP code, and hold through the short silence while the call is passed to the company.

Describe what you can see — where the water is coming from, how long it has been there, and whether it smells — the more specific you are, the faster the right company is on the line. If the source is a pipe or an appliance, shut the main water valve first. Have four things ready and the call goes quickly: the address, when the water started, what is wet now, and whether you have filed an insurance claim.

Still not sure which of these is your situation? (888) 840-6512 · toll-free · answered 24/7

Sources

  1. EPA WaterSense — Fix a Leak Week
  2. EPA — A Brief Guide to Mold, Moisture, and Your Home

Methodology: How we source and verify data · Report an error

How we chose these picks

  • Every pick is a current listing. Stock, star ratings and rating counts are read from Amazon by script and carry the date they were read.
  • Nothing under 4.0 stars makes the list, and the top pick needs a large rating count, so one good week of reviews cannot put it there.
  • Specs are quoted from the listing or the maker, with the test condition behind the number where there is one, and sized against the job rather than the room on the box.
  • We do not run lab or field tests. Where a spec matters, we say what it is measured under and what it cannot tell you.

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