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

A fill valve is failing if the toilet runs continuously into the overflow tube and lowering the float does not stop it, if it hisses, shudders or whistles while refilling, if it fills very slowly or in fits and starts, or if it will not shut off cleanly. Do the overflow check first: take the tank lid off and look at the open center tube — if water is running over its rim, the valve is not shutting off or the level is set too high. If the overflow tube is dry and water is trickling into the bowl, the flapper is the culprit instead, not the fill valve.

Are toilet fill valves universal?

Modern adjustable-height fill valves are effectively universal — one $10 to $25 unit fits almost every US toilet made in the last 40 years, because the valve height telescopes to match your tank and it threads onto a standard shank. The main thing to confirm is that the tank has room for the valve and that you match the water level to the manufacturer's mark. Older ballcock-style valves with a float ball on an arm are usually best replaced with a modern cup-style valve rather than matched like-for-like.

How do I set the water level on a new fill valve?

Set it about one inch below the top of the overflow tube — most tanks have a molded fill line, and the valve packaging states the target. On a cup-style valve you adjust the height by pinching a clip on the side rod and sliding the float cup up or down, or by turning an adjustment screw on top. Too high and water spills into the overflow tube and the toilet runs; too low and the bowl does not refill enough for a clean flush. Set it, flush, and fine-tune.

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

Check three things. First, the water level — if it is above the overflow tube, lower the float so it shuts off below the rim. Second, the flapper — a fill valve replacement does not fix a leaking flapper, and a slow flapper leak makes the valve cycle on every 15 to 30 minutes; run a dye test to confirm the flapper seals. Third, the refill tube — if it is pushed too far down into the overflow tube it can siphon and cause continuous running, so clip it to the rim instead of inserting it deep.

Do I need a plumber to replace a toilet fill valve?

No — this is one of the easier plumbing repairs, entirely inside the tank, with no permit and no risk to the pressurized supply beyond the shutoff. The whole job is shutting off the water, draining and sponging the tank, unscrewing the old valve, dropping in the universal replacement, and setting the level. Call a plumber only in the rare case that the shutoff valve behind the toilet is seized or the tank itself is cracked, neither of which is about the fill valve.

How to Replace a Toilet Fill Valve: 20-Minute Tank Repair

Written & researched by Priya Anand DIY & Tools Editor

Updated August 2026

Over-the-shoulder view of a person's hands tightening a fitting under a kitchen sink with a wrench, in warm evening lamplight

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Replacing a toilet fill valve is an easy DIY repair — about 20 minutes, $12 to $25 for a universal valve, basic tools, no permit and no plumber. If your toilet runs into the overflow tube, hisses, or fills slowly, the fill valve is the likely cause. You shut off the water, drain and sponge the tank, unscrew the old valve, drop in an adjustable universal replacement, and set the water level about an inch below the overflow tube. The only thing that stops this being DIY is a seized shutoff valve or a cracked tank.

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How to Replace a Toilet Fill Valve — The Home Depot

First, confirm it is the fill valve

Take off the tank lid and look at the overflow tube — the open vertical pipe in the middle. If water is spilling over its rim, the valve is not shutting off or the level is too high (a fill-valve or adjustment issue). If the overflow tube is dry but water trickles into the bowl, the flapper is leaking instead. Fix the right part.

Three-quarter view of a person's hands tightening a fitting under a kitchen sink with a wrench, in soft overcast light

Tools and materials

A universal adjustable-height fill valve.
Adjustable pliers or a wrench, a sponge, a small bucket and towels.
Optional: a new braided supply line while the water is off.
Basic hand tools — see best plumbing tools.

Step 1: Shut off and empty the tank

Close the shutoff valve behind the toilet and flush, holding the handle to drain the tank. Sponge out the last inch of water so nothing spills when you disconnect the valve. Disconnect the supply line from the bottom of the tank.

Over-the-shoulder view of a person's hands tightening a fitting under a kitchen sink with a wrench, in soft overcast light

Step 2: Remove the old fill valve

Under the tank, unscrew the locknut that secures the fill valve shank (where the supply line attached). Hold the valve inside the tank so it does not spin. Lift the old valve straight out of the tank. Wipe the area around the shank hole clean.

Step 3: Set the new valve height and install it

Before installing, adjust the new valve's height so the top of it will sit at least one inch above the overflow tube — cup-style valves telescope or twist to set this. Drop the valve through the tank hole, seat its base washer, and hand-tighten the locknut underneath, then a quarter to half turn with pliers. Do not overtighten — the shank is plastic and cracks. Clip or connect the refill tube to the overflow tube rim, not deep inside it, to prevent siphoning.

Step 4: Reconnect water and set the level

Reconnect the supply line — hand-tight plus a quarter turn. Open the shutoff slowly and let the tank fill. Set the water level about one inch below the top of the overflow tube using the float clip or adjustment screw. Flush and watch: the tank should refill and shut off cleanly, with no water entering the overflow tube.

Wide view of a person's hands tightening a fitting under a kitchen sink with a wrench, in soft overcast light

Step 5: Check for leaks and running

Feel the shank connection under the tank for weeping and watch the valve shut off completely. Come back after 20 to 30 minutes — if the toilet cycles on by itself, the flapper is leaking (run a dye test) or the refill tube is siphoning. A correctly set valve shuts off silently and stays off.

Common mistakes

Setting the water level above the overflow tube, so the toilet runs continuously.
Pushing the refill tube deep into the overflow tube, which siphons and causes phantom running.
Overtightening the plastic shank nut and cracking it.
Replacing the fill valve when the flapper was the real problem — always diagnose first.

When to call a plumber

This is DIY for nearly everyone; there is no permit. Call a plumber only if the shutoff valve behind the toilet is corroded and will not close or weeps when you try, or if you find a crack in the tank china — a cracked tank is not repairable and the toilet should be replaced. A wasted, continuously running toilet is worth fixing quickly: the EPA puts a leaking toilet at up to 200 gallons a day.

Related: how to replace a toilet flapper, how to adjust the toilet water level, and how to stop a toilet from running.

How to Replace a Toilet Fill Valve