How to fix a running toilet

Why does a toilet keep running?

Most running toilets trace back to one of two parts inside the tank. The flapper is the rubber seal at the bottom that holds water in the tank and releases it into the bowl when you flush, and the EPA's WaterSense program says old or worn flappers cause most toilet leaks. When the flapper leaks, the tank level drops and the fill valve turns the water back on to refill it, which is why you may hear the toilet refill by itself even though nobody flushed. The repair parts maker Korky describes this pattern and notes that it usually means the flapper or flush valve seal is worn.

The second cause is a fill valve that keeps running after the tank is full. Kohler lists three reasons for a toilet that runs constantly: a binding trip lever arm, water overflowing into the overflow tube of the flush valve, or debris lodged under the cap of the fill valve. The New York City Department of Environmental Protection adds that a change in your home's water pressure can leave a fill valve stuck open. Before you start looking, lift the tank lid and set it down flat on a folded towel out of the way.

How to tell whether the flapper or the fill valve is leaking

For a simple first check, the EPA recommends a dye test: placing a few drops of food coloring in the tank and checking the bowl after 10 minutes without flushing. If any color shows up in the bowl, the tank is leaking into it, which points to the flapper. Flush right after the test so the dye does not stain the tank.

A pencil mark on the tank wall helps you separate the two causes. NYC DEP suggests marking the actual water level on the back wall of the tank, flushing, and watching the refill. If the water rises above the mark and then goes down afterward, the flapper is probably leaking. If it stays below the mark and then rises above it, the fill valve is probably faulty. Korky offers a slower version: mark the level, turn off the supply valve behind the toilet, and wait at least 25 minutes. A drop below the mark means a part in the tank is leaking, and if the level falls only to the flapper, the flapper or seal needs replacing, while a drop to the overflow tube or the tank bottom means the flush valve itself needs replacing.

Step 1: Check the chain and the water level

Before you buy any parts, check two adjustments that Kohler lists among its corrective actions. Kohler says the chain between the trip lever and the flapper should have roughly one to two links of slack, and Korky gives the same guidance. A chain that is too loose can drop under the flapper and keep it from sealing, and a chain that is too tight can hold the flapper open. Remove excess chain if needed and make sure the trip lever moves freely.

Next, look at the water level, because if water spills into the overflow tube, Kohler says to adjust the tank water level so it no longer overfills. Kohler's troubleshooting guide asks you to match the water level to the waterline mark molded inside the tank. The way you lower the level differs from one fill valve to another, so follow the instructions printed on the valve or in the toilet's manual. Flush and watch the refill to confirm the water stops below the top of the overflow tube.

Step 2: Replace a worn flapper

The EPA says flappers should be checked periodically and replaced at least every five years, because the rubber wears out. NYC DEP notes that chlorine tablets and other in-tank cleaners can corrode the flapper and other rubber parts, and that the damage is worse when a toilet goes unflushed for a long time.

1. Turn off the supply valve behind the toilet and flush to empty the tank.
2. Unhook the chain from the trip lever and remove the old flapper from its mounts on the flush valve.
3. Take the old flapper to the store or look up your toilet's model number, since Korky advises matching the size of the flush valve opening, and tower or canister valves need a seal made for that model.
4. Check the flush valve seat for debris, mineral deposits, or cracks, and clean it so the new flapper can seal.
5. Install the new flapper, reattach the chain with one or two links of slack, turn the water back on, and repeat the dye test.

Step 3: Clean or replace the fill valve

If the flapper seals and water keeps running after the tank is full, Korky says the float may be stuck or the valve may be failing. Kohler recommends flushing debris out of the fill valve first, which is common after a new installation or after the water supply has been shut off and turned back on, since that can loosen sediment in the lines. Kohler's videos show the job with nothing more than a plastic cup, and the steps for your valve are in its instructions.

Replace the fill valve if the toilet still runs after cleaning, or if the float sinks. NYC DEP recommends against replacing an old fill valve that has a float ball with another float-ball valve, and suggests a newer piston-type fill valve instead. The replacement part varies with the toilet model, so find the model number before you buy. If you would prefer not to do this repair, NYC DEP advises calling a licensed plumber.

How much water does a running toilet waste?

The amount of water lost depends on which part is leaking. NYC DEP says water can flow through an open fill valve at three to five gallons per minute, which can reach 4,000 gallons in a day. A worn flapper leaks more slowly, and the EPA says it can silently waste thousands of gallons a year. The EPA also estimates that household leaks can waste 180 gallons per week, often from toilets, and that fixing easily corrected leaks can save homeowners about 10 percent on their water bills. To check the whole house, the EPA suggests reading your water meter before and after a two-hour period when no water is used, since any change points to a leak somewhere.

NYC DEP recommends testing each toilet in your home for leaks once a year, which fits easily into a seasonal home maintenance checklist. You will find more bathroom projects in the bathroom section.

What if the toilet has no tank or still runs?

Some homes have flushometer-valve toilets with a hand valve on a pipe from the wall and no tank. NYC DEP says moving water in the bowl after a flush means the valve is leaking and needs repair or replacement, and that phantom flushes caused by pressure changes should be investigated by a licensed plumber.

On a tank toilet that keeps running after you have replaced the flapper, reset the chain, and serviced the fill valve, Korky points to the flush valve drain opening. Clean off any mineral deposits you find there, and replace the flush valve if you see cracks, warping, or other damage, which on a two-piece toilet involves removing the tank. That job takes more time and care than the other repairs in this guide, so it is a reasonable point to bring in a licensed plumber if you have not removed a toilet tank before.