What a toilet float does and when to replace it

A toilet float is the hollow ball or cup that rises and falls with the water level in your tank. When the tank fills after a flush, the float rises and shuts off the fill valve—the mechanism that stops water from entering. When the float gets stuck, cracks, or fills with water, it can't rise properly, so the tank either runs constantly or won't fill at all. Replacing it is a straightforward job that takes about 15 minutes and costs $10 to $30 for the part.

You'll know the float is the problem if water runs into the overflow tube (the hollow pipe in the center of the tank) even when nobody has flushed, or if the tank won't fill past a certain level. Before you replace it, turn off the water at the shutoff valve behind the toilet—turn the knob clockwise until it stops. Flush once to empty the tank, then you're ready to work.

Key Takeaways

  • Turn off the water at the shutoff valve behind the toilet before you start any work inside the tank.
  • The float connects to the fill valve with a rod or clip; you'll need to disconnect this before removing the old float.
  • Bring the old float to the hardware store to match the size and type, or note the tank model number from inside the lid.
  • The new float installs in reverse order—clip or rod back on, then turn the water back on and test by flushing twice.
  • If water still runs after replacement, the fill valve itself may need cleaning or replacement instead.

Identify which type of float you have

Toilet floats come in two main styles. A ball float is a hollow sphere connected to the fill valve by a long rod that runs horizontally across the tank. A cup float is a cylinder that slides up and down a vertical rod attached to the fill valve. Lift the tank lid and look at what's inside—the style you see is the one you need to replace.

If you have a ball float and it's cracked or waterlogged (it sinks instead of floats), you'll see water inside it. Cup floats fail less often but can get stuck or crack the same way. Either type can be replaced with the same type or swapped for the other—both work equally well, though cup floats are slightly more reliable because they're less likely to get knocked off balance.

Remove the old float

With the water off and the tank empty, look at how the float connects to the fill valve. On a ball float, you'll see a horizontal rod running from the float to the valve—this rod is usually held in place by a clip or pin. Squeeze or unclip this connector and slide the rod out. The float will come free.

On a cup float, the cylinder slides onto a vertical rod. Push down slightly on the float and twist it counterclockwise, or straightforward slide it straight up and off the rod—the method depends on the brand. Once the float is off, set it aside. You don't need to remove the rod or valve itself.

Get the right replacement float

Take the old float to a hardware store or home center and show it to someone in the plumbing section. They can match it by size and type. If the float is too damaged to carry, note the toilet tank model number instead—it's usually stamped on the inside of the lid or on the back of the tank. The staff can look up what float fits that model.

Floats are inexpensive and come in standard sizes. You'll find them in the plumbing aisle near fill valves and tank repair kits. Most hardware stores stock ball floats and cup floats separately, so make sure you're buying the type you need. If you're unsure, ask the staff—they handle this question constantly.

Install the new float

Slide the new float onto the rod or into the connector the same way the old one came out. If it's a ball float with a horizontal rod, insert the rod through the clip on the fill valve and find it with the pin or clip. The float should move freely up and down without binding. If it catches or feels tight, remove it and check that the rod is straight—a bent rod will cause the same problem you just fixed.

For a cup float, slide it onto the vertical rod and twist clockwise until it seats, or push it down until it clicks into place—again, the exact method depends on your toilet's design. The float should move smoothly from bottom to top without sticking. Once it's installed, turn the water back on at the shutoff valve by turning the knob counterclockwise.

Test and adjust the water level

Let the tank fill completely, then flush. Watch the float rise as the tank refills—it should shut off the water when the tank is full. The water level should be about an inch below the overflow tube. If water is running into the overflow tube, the float isn't rising high enough, which means either the float is still waterlogged (unlikely if it's new) or the fill valve needs adjustment.

Most fill valves have an adjustment screw or clip on top. If the water level is too low, turn the adjustment screw counterclockwise a quarter turn to raise the float's shutoff point. If it's too high, turn it clockwise. Make small adjustments and test after each one. Flush twice to confirm the tank fills and shuts off correctly both times.

When the float replacement doesn't fix the problem

If you've installed a new float and water still runs into the overflow tube, the fill valve itself is likely worn or dirty. Sediment can prevent the valve from sealing completely, even when the float is working. You can try cleaning the valve by turning off the water, removing the fill valve cap (usually by turning it counterclockwise), and rinsing it under running water to flush out debris.

If cleaning doesn't work, the fill valve will need replacement—a job similar in difficulty to float replacement but slightly more involved. You can find fill valve kits at any hardware store, and the instructions come in the box. If you'd rather not tackle that, a plumber can replace it in under an hour for a service call fee plus the part cost.

Frequently Asked Questions

Can I replace the float without turning off the water?

You can, but you'll get wet. The tank will drain when you remove the float, and water will spill out as you work. Turning off the water takes 10 seconds and keeps your bathroom dry, so it's worth doing.

What if the float is stuck and won't come out?

The rod or clip may be corroded. Spray it with penetrating oil (like WD-40) and wait 15 minutes, then try again. If it's still stuck, gently tap the connector with a rubber mallet to break the corrosion loose. Don't force it hard enough to crack the tank.

Is a ball float or cup float better?

Cup floats are slightly more durable because they're less likely to get knocked off balance. Ball floats are cheaper and equally effective if the rod stays straight. Either will last several years. Choose whichever type you had unless you had repeated problems, in which case try the other style.

Do I need to drain the tank before I start?

Yes. After you turn off the water, flush once to empty it. If you try to work in a full tank, water will spill everywhere and you won't be able to see what you're doing.

How do I know if the float is actually broken?

A ball float that sinks is definitely broken—it's filled with water. A float that's cracked will also sink or feel heavy. If the float looks fine but water still runs, the problem is likely the fill valve, not the float. Try the float replacement first since it's cheaper and easier, but be prepared that you might need the valve cleaned or replaced instead.