How to Replace a Toilet Float: Ball, Cup and Fill-Valve Types

A toilet that runs nonstop, hisses between flushes or fills so slowly you give up waiting usually has a float problem. Learning how to replace a toilet float takes about 20 minutes once you know which kind of float your tank uses, and the part costs less than a takeout lunch. The tricky bit is that “float” means two very different things depending on the age of the toilet.

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Older toilets use a ballcock valve with a hollow float ball on a long metal or plastic arm. When the ball fills with water or the arm bends, the valve never shuts off. Newer toilets use a cup float that slides up and down the fill valve shaft. On cup-style valves the float is usually molded into the valve, so replacing the float really means replacing the whole fill valve. Both jobs start the same way: shut off the water, flush to empty the tank and work in a dry tank.

If you only need to change the water level, adjustment may be enough. If the float is cracked, waterlogged, stuck or the valve keeps running after adjustment, replacement is the fix.

How to Replace a Toilet Float: Identify Your Float Type

Lift the tank lid and set it on a towel somewhere it cannot fall. Porcelain lids crack easily. Look at the valve on the left side of the tank, the one connected to the water supply from below.

• Ball-and-arm float (ballcock). A round ball, usually 4 to 5 inches across, on a rod 8 to 12 inches long. The rod screws into a lever at the top of a brass or plastic valve. Common in toilets from before the 1990s.
• Cup float. A cylindrical float that rides on the valve shaft itself. A metal clip or adjustment screw on a vertical rod sets the height. This is the most common modern design.
• Floatless or pressure-sensing valve. A compact valve near the bottom of the tank with no visible float. Water pressure inside the tank tells it when to shut off. These are adjusted with a dial and replaced as a unit.
• Side-mounted float cup. A small float on a short arm beside the valve shaft. Again usually molded into the valve.

Check also whether the overflow tube, the open pipe in the center of the tank, has water spilling into it. If the water level rises above the top of that tube, the float is set too high or the valve is not shutting off.

Tools and Materials

• Replacement float ball and arm, or a universal toilet fill valve for cup-style toilets
• Adjustable wrench or channel-lock pliers
• Sponge, bucket and old towels
• Rubber gloves
• Small flat screwdriver
• New flexible supply line (recommended if the old one is more than five years old)
• Scissors or utility knife to trim the refill tube

Step 1: Shut Off and Drain the Tank

1. Turn the supply valve behind the toilet clockwise until it stops. If the valve is stiff or weeps, do not force it; shut the main water supply instead.
2. Flush and hold the handle down to empty the tank.
3. Sponge out the remaining inch or so of water. Wear gloves, and wring the sponge into a bucket.
4. Put a towel on the floor under the supply connection to catch drips.

Step 2A: Replace a Ball Float and Arm

The simplest repair on old ballcock toilets is swapping the ball itself.

1. Unscrew the ball from the end of the arm by turning it counterclockwise. Shake it: if you hear water sloshing inside, it is waterlogged and sinking, which is exactly why the valve kept running.
2. Inspect the arm. If it is corroded, bent unevenly or the threads are stripped, unscrew it from the ballcock lever and replace it too.
3. Thread the new arm into the lever, then screw the new ball onto the arm until snug. Do not overtighten plastic threads.
4. Gently bend the arm downward near the middle if you need a lower water level, or use the adjustment screw on the ballcock if it has one.

Plenty of plumbers recommend going one step further on a very old ballcock: replace the entire valve with a modern fill valve. Brass ballcock seals wear out, and a new valve is quieter, refills faster and costs only a little more than a ball and arm kit.

Step 2B: Replace a Cup Float by Swapping the Fill Valve

On most cup-style toilets you cannot buy the float separately, so the repair is a full fill valve swap. A universal fill valve fits the vast majority of two-piece toilets and adjusts in height to suit tall and short tanks.

1. Disconnect the supply line. Unscrew the coupling nut under the tank where the supply line meets the valve shank. Expect a cup of water to drip out.
2. Remove the locknut. Under the tank, unscrew the large plastic locknut that holds the valve to the tank. Hold the valve from inside the tank so it does not spin.
3. Lift out the old valve. Pull the valve straight up and out, and unclip the refill tube from the overflow pipe.
4. Clean the tank hole. Wipe away mineral deposits and old gasket residue so the new gasket seals flat.
5. Set the height. Adjust the new valve so the critical level mark (often labeled CL) sits at least 1 inch above the top of the overflow tube. Most universal valves twist to telescope.
6. Install the valve. Insert it with the cone washer seated in the tank hole, then hand-tighten the locknut from below plus a quarter turn with pliers. Overtightening can crack porcelain.
7. Attach the refill tube. Clip it to the overflow tube so the end sits above the water line, not submerged. A submerged refill tube siphons water and causes phantom running.
8. Reconnect the supply. Hand-tighten the supply line onto the shank, plus a slight snug with pliers.

Step 3: Restore Water and Set the Level

Open the supply valve slowly and watch the tank fill. The water should stop about 1 inch below the top of the overflow tube, or at the waterline mark molded inside the tank. On a cup float, squeeze the clip and slide the float up or down, or turn the adjustment screw. On a ball float, bend the arm slightly or turn the screw on the ballcock.

Flush several times and check under the tank for drips at the locknut and supply connection. Wipe the connections with a dry tissue; any damp spot means a quarter turn more is needed.

Troubleshooting After Replacing the Float

• Toilet still runs. Check the flapper at the bottom of the tank. A warped or mineral-crusted flapper lets water leak into the bowl, and the valve keeps refilling. Add a few drops of food coloring to the tank; if color appears in the bowl within 15 minutes without flushing, replace the flapper.
• Water overflows into the overflow tube. The float is set too high. Lower it.
• Weak flush. The float is set too low, so the tank holds too little water. Raise it toward the waterline mark.
• Valve hisses or squeals. Debris may have entered during the install. Shut off the water, remove the valve cap per the instructions and flush the valve by holding a cup over it while briefly opening the supply.
• Float rubs the tank wall. Rotate the valve slightly before tightening the locknut, or reposition the float arm.
• Slow refill. The supply valve may not be fully open, or the supply line may be kinked or clogged with sediment.

Cost and Time

A float ball and arm kit typically costs $5 to $15. A universal fill valve usually runs $10 to $30, and a braided supply line adds $5 to $15. The job takes 15 to 45 minutes depending on how stubborn the old locknut is. A plumber’s service call for the same work usually lands in the range of $100 to $250, mostly for the trip.

Cleaning and Safety Notes

While the tank is empty, it is a good time to scrub mineral buildup from the tank walls. Use a mild cleaner made for toilet tanks or white vinegar, and never mix cleaners, especially bleach with ammonia or acidic products, which releases toxic gas. Avoid drop-in tank tablets with strong bleach; they can degrade rubber seals and the new float valve faster.

If the shutoff valve behind the toilet leaks when you turn it or will not close, replacing that valve is a plumbing job that requires shutting off the main supply. Call a plumber if you are not comfortable with that step or if the supply pipe is old galvanized steel.

When a Float Swap Is Not Enough

Sometimes the float is fine and the problem is elsewhere. A cracked tank, a corroded flush valve seat or a leaking tank-to-bowl gasket all produce symptoms that look like float failure. If water appears on the floor, if the tank has hairline cracks or if the toilet keeps running with a new valve and new flapper, the toilet may need a full flush valve rebuild or replacement. Knowing how to replace a toilet float solves most running-toilet complaints, but a persistent leak after the repair is worth a professional look before it damages the floor.

Once you have done this repair once, the next one goes quickly. Keep the instruction sheet from the new valve in a drawer, and note the date so you know how old the parts are next time the toilet starts running.