A fill valve replacement takes about 30 minutes and costs $15 to $30 in parts

The fill valve (also called a ballcock or inlet valve) is the mechanism that refills your toilet tank after you flush. When it fails, your toilet either runs constantly, fills too slowly, or doesn't fill at all. Replacing it is a straightforward job you can do yourself with basic tools — no plumber needed unless the valve is stuck or the tank is cracked.

The entire process involves shutting off the water, draining the tank, unbolting the old valve from underneath, and screwing in a new one. Most modern fill valves are universal and fit any standard toilet. You'll need an adjustable wrench, a flathead screwdriver, and about 30 minutes of your time.

Key Takeaways

  • Turn off the water supply at the shutoff valve behind or below the toilet, then flush to empty the tank completely.
  • The fill valve bolts to the bottom of the tank from inside; you'll access the nut from underneath using an adjustable wrench.
  • Universal fill valves cost $15 to $30 and fit any standard toilet — brands like Fluidmaster and Korky are widely available at hardware stores.
  • After installing the new valve, adjust the water level by turning the adjustment screw or clip on top of the valve until water stops about one inch below the overflow tube.
  • If the shutoff valve is stuck or leaking, or if you crack the tank during removal, call a plumber rather than forcing it.

Locate the shutoff valve and turn off the water

Look behind or below the toilet for a small oval knob attached to a copper or plastic pipe coming from the wall. This is your shutoff valve. Turn it clockwise until it stops — you should feel resistance, but do not force it. If the valve is stuck or leaks when you turn it, stop and call a plumber; forcing a stuck valve can break it and flood your bathroom.

Once the water is off, flush the toilet to empty the tank. If water remains in the tank after flushing, use a sponge or towel to soak it up and wring it into a bucket. You need the tank completely dry so you can see what you're doing and avoid water damage to your floor.

Disconnect the water supply line

The water supply line is the flexible hose or rigid pipe that runs from the shutoff valve to the bottom of the toilet tank. At the toilet end, it connects with a nut — usually a large plastic or brass fitting. Use your adjustable wrench to turn this nut counterclockwise and loosen it by hand. Water may drip out, so have a bucket or towel ready.

Once the nut is loose, unscrew it the rest of the way by hand and pull the supply line away from the tank. Set it aside where it won't roll away — you'll reconnect it to the new valve later.

Remove the old fill valve from the tank bottom

Reach under the toilet tank and locate the large nut holding the fill valve in place. This nut is on the underside of the tank, directly below where the valve sits inside. Use your adjustable wrench to turn this nut counterclockwise. It may be tight, so grip the wrench firmly and turn slowly. As you loosen it, hold the valve stem (the part sticking up inside the tank) steady with your other hand so the valve doesn't spin.

Once the nut is loose enough, finish unscrewing it by hand. The old valve will now lift out from inside the tank. You may see a rubber or foam gasket (a seal) around the hole — pull this out too and discard it. Wipe the hole clean with a dry cloth before installing the new valve.

Install the new fill valve

Most universal fill valves come with a new gasket already attached or included in the box. If yours is separate, slide the gasket onto the valve stem first. Then insert the new valve into the hole from inside the tank, pushing it straight down until the threaded part pokes through the bottom.

Reach underneath and thread the nut onto the valve stem by hand first — this prevents cross-threading. Once it's hand-tight, use your adjustable wrench to turn it clockwise another quarter to half turn. Do not over-tighten; you only need it snug enough that water won't leak around the gasket. If you over-tighten, you risk cracking the tank.

Reconnect the water supply line

Take the supply line you disconnected earlier and thread the nut onto the bottom of the new fill valve. Hand-tighten it first, then use your wrench to snug it another quarter turn. Again, snug is the goal — not maximum force. Turn the shutoff valve counterclockwise to restore water to the tank and watch for leaks around both connections (the tank bottom and the supply line).

A small drip usually stops once the rubber gasket settles; if water streams out, turn off the water and tighten the nut slightly more. Check both connection points before moving on. Once you see no active leaks, you're ready to adjust the water level.

Adjust the water level and test the fill

As the tank fills, watch the water level. It should stop about one inch below the top of the overflow tube — the hollow pipe standing upright inside the tank. Most modern fill valves have an adjustment screw or clip on top that controls this level. Consult the instructions that came with your valve for the exact adjustment method, as it varies by brand.

Once the tank is full, flush it and listen. The fill valve should shut off cleanly when the tank reaches the correct level, and you should hear no hissing or running water after the tank is full. If water continues to run into the overflow tube, the water level is too high — lower it by adjusting the valve. If the tank doesn't fill completely, raise the water level. After you adjust, flush again to test.

Frequently Asked Questions

What if the fill valve nut won't budge?

explore penetrating oil (like WD-40) around the nut and wait 15 minutes, then try again with your wrench. If it still won't move, stop — forcing it risks cracking the tank. Call a plumber instead; they have tools to remove stuck valves without damage.

Can I use any fill valve, or does it have to match my toilet brand?

Universal fill valves work in nearly all standard toilets regardless of brand. Fluidmaster and Korky are common brands sold at hardware stores. Avoid buying a valve made specifically for a rare or very old toilet unless you know your model number.

Why is water still running into the overflow tube after I adjust the level?

The fill valve may not be closing properly. Check that the adjustment is set correctly and that nothing is blocking the valve seat inside the tank. If water continues to run after adjustment, the new valve may be defective — return it and try another one.

Do I need to turn off the water at the main shutoff if the toilet shutoff valve doesn't work?

Yes. If the shutoff valve behind the toilet is stuck or leaking, locate your home's main water shutoff (usually in the basement, crawlspace, or outside) and turn it off there instead. Then you can safely work on the toilet.

What if I crack the tank while removing the old valve?

Stop when ready and turn the water back on at the shutoff valve. A cracked tank cannot be repaired and must be replaced — call a plumber to remove the old toilet and install a new one.