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

A running toilet is almost always one of four things: a flapper that does not seal, a chain that is too tight or too slack, a water level set too high, or a worn fill valve. You can check and fix all four with basic hand tools, usually in under an hour.

Quick answer

Work in this order, because each step is cheaper and faster than the next:

1. Jiggle the handle. If the running stops, check the chain and handle.
2. Do a dye test to see whether water is leaking from the tank into the bowl.
3. Check the water level against the overflow tube and adjust the float.
4. Replace the flapper if it is worn, or the fill valve if water never stops entering the tank.

What causes a running toilet

The tank holds water behind a rubber flapper. When you flush, the flapper lifts, the tank empties into the bowl, then the flapper drops back and the fill valve refills the tank. If any part of that cycle fails, water keeps moving.

Symptom	Likely cause	Fix
Runs until you jiggle the handle	Chain too short or too long, loose handle	Adjust chain length, tighten handle nut
Dye shows up in the bowl	Worn or misaligned flapper, dirty valve seat	Clean seat, replace flapper
Water trickles down the overflow tube	Water level too high	Lower the float
Water keeps entering and never stops	Float stuck or fill valve worn out	Adjust float, then replace fill valve
Toilet refills by itself every few minutes (“ghost flushing”)	Slow flapper leak	Replace flapper

What you need

• A few drops of food coloring or a dye tablet
• A replacement flapper (if the dye test shows a leak)
• A screwdriver and adjustable pliers
• Fine sandpaper or a scouring pad for the flapper seat
• A towel and a small bucket or sponge

Take the old flapper, or a clear photo of it, to the store. Check its width and whether it has a foam float, since the replacement should match.

Step 1: Run the dye test

This test tells you whether the leak is between the tank and the bowl.

1. Remove the tank lid and set it somewhere safe.
2. Add a few drops of food coloring (or one dye tablet) to the tank. Do not flush.
3. Wait at least 15 minutes. Guidance varies from 10 to 20 minutes, and the longer end catches slow leaks.
4. Look in the bowl. Colored water means the flapper or its seat is leaking. Clear water points toward the handle, chain or water level.
5. Flush afterward so the dye does not stain the tank.

Step 2: Check the handle and chain

If you have to jiggle the handle to stop the running, look for these problems:

• Chain too short. It holds the flapper slightly open.
• Chain too long. Slack can slip under the flapper and stop it from closing. A chain caught under the flapper is a known source of waste.
• Kinked chain. Replace it with a ball-type chain.
• Loose handle. Tighten the nut that holds the handle to the tank. If it still sticks, replace the handle.

Set the chain so there is only a little slack when the flapper is closed. Flush a few times to confirm the flapper drops fully into place.

Step 3: Set the water level and float height

With the tank full, look at the overflow tube, the open pipe in the middle of the tank. Water should stop about 1/2 to 1 inch (1.5 to 2.5 cm) below its top. If water is spilling into the tube, the toilet will run constantly.

How you adjust depends on the fill valve type:

Fill valve type	How to lower the water level
Float cup on a vertical rod	Squeeze the spring clip and slide the float down the rod, or turn the adjusting screw clockwise
Float ball on a metal arm	Turn the screw where the arm meets the valve, or gently bend the arm down

Also check the small refill tube. Its end should sit inside the overflow tube and no deeper than about 2 inches (5 cm), so it does not siphon water back.

Flush and watch where the water stops. If the level stays high after adjusting, the float may be waterlogged or the whole fill valve may be worn out and need replacing.

Step 4: Replace the flapper

The flapper is the most common cause of leaks, and replacing it is a quick job. Rub the underside of the old one. If it leaves rubber streaks on your fingers or feels hard, replace it.

1. Turn off the water at the wall shutoff valve (the valve near the floor behind the toilet) by turning it clockwise.
2. Flush to empty the tank. Note how the chain is attached and how much slack it has.
3. Unhook the old flapper from the overflow tube ears and from the chain.
4. Clean the valve seat, the ring the flapper sits on. Remove any corrosion or mineral buildup, and smooth it with fine sandpaper. Dry it.
5. Install the new flapper and attach the chain with the same slack as before.
6. Turn the water on, let the tank fill, and repeat the dye test.

In the UK and Australia the tank is usually called the cistern, and the flapper may be sold as a flush valve seal or washer. Dual-flush toilets often have a seal at the base of the central canister instead. Use the exact part the manufacturer specifies.

Step 5: Replace the fill valve if needed

If the water never stops entering the tank, even after adjusting the float, the fill valve has likely worn out. Replacement kits come with instructions for each model. Turn off the water supply and empty the tank before starting, and use a kit that fits your tank. If you are not comfortable removing the supply line, this is a good point to call a plumber.

Common mistakes

• Skipping the dye test. You may replace a part that was not the problem.
• Buying the wrong flapper. Sizes and styles differ, so match the old one.
• Leaving the water level too high. It looks fine but quietly spills into the overflow tube.
• Using in-tank bowl cleaners. Time-released tablets and strong chlorine cleaners can shorten the life of rubber parts. If you use them, check for leaks more often.
• Forgetting the seat. A new flapper will still leak on a corroded or gritty seat.
• Replacing the flapper only once it fails. Treat it as routine upkeep every 3 to 5 years.

When to call a professional

Call a plumber if the shutoff valve will not close or leaks, the supply line is corroded, the tank is cracked, water is leaking onto the floor, or the toilet still runs after you have replaced the flapper and fill valve. Sometimes the cost of repeated repairs on an old toilet approaches the cost of a new, more efficient one, and a plumber can help you decide.

Sources

• Fix a Toilet Leak, Portland Water Bureau
• Toilet Leaks and Repair Guide, City of Calgary
• Fix a Leak Week, US EPA WaterSense