How to Fix a Running Toilet: Flapper, Fill Valve, and Float

A running toilet wastes up to 200 gallons of water per day and can add $50-$100 per month to your water bill if left unaddressed. The good news: learning how to fix a running toilet is one of the easiest home repairs you can tackle, and the parts cost $5-$25 at most. Nearly every case traces back to one of three components inside the tank: the flapper, the fill valve, or the float.

Diagnose the Problem First

Remove the tank lid and watch what happens after a flush. If water continuously trickles into the bowl, the flapper is not sealing. If the fill valve runs nonstop and water flows into the overflow tube, the float is set too high or the fill valve is failing. If you hear intermittent cycling (the toilet “ghost flushes” every few minutes), a slow leak past the flapper is gradually lowering the tank level until the fill valve kicks in to refill.

Drop a few drops of food coloring into the tank and wait 15 minutes without flushing. If colored water appears in the bowl, the flapper is leaking. This simple test pinpoints the problem in minutes and tells you exactly which repair to make.

Fix 1: Replace the Flapper

The flapper is a rubber or silicone seal that sits over the flush valve opening at the bottom of the tank. Over time, the rubber degrades from constant water exposure and chlorine in municipal water, losing its ability to form a tight seal. Flappers are the most common cause of a running toilet and cost $5-$10 to replace.

1. Shut off the water supply valve behind the toilet (turn clockwise).
2. Flush the toilet to empty the tank.
3. Unhook the old flapper from the pegs on either side of the flush valve and disconnect the chain from the flush handle lever.
4. Bring the old flapper to the hardware store to match the size. Most toilets use a 2-inch or 3-inch flapper.
5. Hook the new flapper onto the pegs and connect the chain to the handle lever. Leave about half an inch of slack in the chain, enough that the flapper sits flat but the chain is not so tight that it holds the flapper slightly open.
6. Turn the water back on and let the tank fill. Watch for leaks.

Fix 2: Adjust the Float

The float tells the fill valve when to stop adding water. If it is set too high, water rises above the overflow tube and runs continuously into the bowl. Modern toilets use one of two float types: a cup float that slides up and down the fill valve shaft, or a ball float on the end of a metal arm.

For cup floats, pinch the spring clip on the float and slide it down the shaft about half an inch. For ball floats, bend the metal arm slightly downward or turn the adjustment screw at the pivot point. The correct water level is about 1 inch below the top of the overflow tube. Mark this level with a pencil on the inside of the tank so you can verify after adjusting.

Fix 3: Replace the Fill Valve

If adjusting the float does not stop the running, the fill valve itself is worn out. Internal seals deteriorate after 5-8 years, causing the valve to leak water past the shutoff point. Universal fill valves like the Fluidmaster 400A ($8-$12) fit nearly every toilet on the market and install in about 15 minutes.

1. Shut off the water and flush the toilet. Sponge out remaining water in the tank.
2. Place a towel under the tank. Disconnect the water supply line from the bottom of the fill valve using an adjustable wrench.
3. Remove the locknut on the outside bottom of the tank that holds the fill valve in place. Lift the old valve out.
4. Adjust the height of the new fill valve so the overflow mark aligns about 1 inch below the overflow tube top. Insert the valve, hand-tighten the locknut, then snug it a quarter turn with pliers.
5. Reconnect the supply line, clip the refill tube to the overflow pipe, and turn the water on. The valve should shut off cleanly when water reaches the set level.

Checking the Flush Valve Seat

Sometimes a new flapper still leaks because the flush valve seat (the ring the flapper presses against) is corroded or has mineral buildup. Run your finger around the seat surface. If it feels rough, pitted, or has hard water deposits, scrub it with fine emery cloth or a Scotch-Brite pad until smooth. A damaged seat that cannot be smoothed requires a complete flush valve replacement ($15-$25), which involves removing the tank from the bowl.

When the Entire Toilet Needs Replacing

Toilets manufactured before 1994 use 3.5-5 gallons per flush compared to the 1.28-1.6 gallons mandated by current federal standards. If your toilet is older than 25 years and needs repeated repairs, replacing the entire unit with a WaterSense-certified model ($100-$300) saves water and eliminates ongoing maintenance headaches. Installation takes 1-2 hours and costs $150-$300 if you hire a plumber, though it is a manageable DIY project for anyone comfortable with basic plumbing connections.

Preventing Future Issues

Replace the flapper every 4-5 years proactively, even if it appears to be working. Drop-in tank tablets containing chlorine or bleach accelerate rubber degradation and should be avoided. If your home has hard water, the mineral scale that builds up on tank components shortens the life of every internal part. A whole-house water softener or periodic vinegar cleaning of the tank internals helps extend the intervals between repairs.