Short answer
A running toilet is usually a worn flapper, a chain with the wrong slack, or a fill valve or float set too high. Put a few drops of food coloring in the tank and wait about 10 minutes without flushing. Color in the bowl means the flapper is leaking. If water will not stop, close the supply valve behind the toilet. Call a plumber for cracks, leaks or stuck valves.
A toilet that keeps running is easy to ignore and expensive to leave. Most causes are inside the tank and are cheap parts that many homeowners can replace. This guide shows how to find which part is at fault, how to do the simple swaps safely, and when to stop and call a plumber.
If your toilet is overflowing, or the bowl is filling with water and not draining, that is a different problem. Read toilet overflowing: what to do first.
Why a toilet running water is worth fixing
The EPA's WaterSense program says an old or worn flapper can cause your toilet to flush on its own or silently leak thousands of gallons a year. It also says the average household's leaks can account for more than 9,300 gallons of water wasted every year, and that 9 percent of homes have leaks that waste 50 gallons or more per day. The EPA gives no per-toilet number on that page, so treat these as general figures, not a measurement of your toilet.
The water also goes somewhere. If you have a septic system, a running toilet sends extra water into the tank and drainfield (see the septic section below).
Know the parts in the tank
Take the lid off carefully and set it somewhere it will not fall. You will see a few parts. Here is what each one does and how it fails.
| Part | What it does | Sign of trouble |
|---|---|---|
| Flapper | Rubber seal at the bottom of the tank that lifts to flush and drops to seal | Color from the dye test appears in the bowl; toilet refills by itself |
| Chain or lift wire | Connects the flush handle to the flapper | Flapper held open, or drops too quickly |
| Fill valve and float | Refills the tank and shuts off when the float reaches the set level | Water keeps running, or creeps up the overflow tube |
| Overflow tube | Tube in the center that carries excess water down so the tank cannot spill | Water level at or above the top of the tube |
| Supply valve | Small valve on the wall or floor behind the toilet that shuts off the water to the tank | Needed for any repair; if it will not turn, do not force it |
Toilet keeps running: how to find the cause
Work through these checks in order.
- Check the water level. H2ouse.org's toilet troubleshooting guide says manufacturers usually suggest setting the level about one inch below the top of the overflow tube. If water is at or above the top of the tube and flowing into it, the fill valve or float is the likely cause.
- Do the dye test. The EPA says to put a few drops of food coloring in the toilet tank. If color appears in the bowl after 10 minutes, the toilet leaks. Do not flush while you wait. Flush right away afterward, because the dye can stain the tank. Some other guides suggest waiting 15 minutes, so a longer wait is fine.
- Look at the chain. Make sure the chain or lift wire is not caught under the flapper and is not holding it open.
- Look at the float and fill valve. See whether the float is stuck against the tank wall or leaking, and whether the water keeps entering after the level is reached.
The EPA says old or worn-out toilet flappers can cause leaks, and that the flapper should be checked periodically and replaced at least every five years.
How to fix a running toilet step by step
These steps cover the most common repair, a flapper that no longer seals. Work slowly and keep towels nearby.
- Turn off the water. Close the supply valve behind the toilet by hand. Do not use a wrench on a stuck valve. If it will not turn, stop and call a plumber.
- Flush once to empty most of the water from the tank.
- Inspect the flapper. Look for a flapper that is warped, cracked, sticky or no longer flat against its seat.
- Buy a match. The EPA suggests bringing the old flapper, or a picture of it, to the hardware store so you can match the replacement to your toilet model.
- Swap the flapper. Unhook the old one, disconnect the chain, and fit the new flapper the same way the old one was fitted. Reconnect the chain with a little slack, not tight. H2ouse says to shorten the chain or wires if the flapper drops too quickly.
- Turn the water back on slowly. Let the tank fill, flush a few times, and watch whether it stops.
- Repeat the dye test to confirm the leak is gone.
Do not hurry the last step. A new part can still leak if the seat it rests on is rough or damaged. H2ouse suggests lightly sanding a rough flush valve seat, but if the seat is cracked or damaged, call a plumber.
Toilet fill valve and float problems
If the flapper seals but the toilet still runs, look at the fill valve and float.
- Water level too high. H2ouse says to lower the level by adjusting the screw on top of the fill valve, or by sliding the clip on the float if your valve uses one. The direction to turn differs between valve designs, so follow the markings or instructions on your valve and make small changes.
- Leaking float ball. H2ouse says to replace a float ball that is leaking.
- Water still creeping up the overflow tube or escaping through the refill tube. H2ouse says to repair or replace the fill valve, and says you are probably better off replacing the entire mechanism rather than only the diaphragm.
Replacing a fill valve involves disconnecting the supply line from the bottom of the tank. Turn off the water first. If connections are corroded, or you are not sure how the parts come apart, a plumber is the safer choice.
When a part swap is simple, and when to call a plumber
| Situation | Reasonable for many homeowners | Call a plumber |
|---|---|---|
| Flapper worn or warped | Yes, with the supply valve off | If the seat is damaged |
| Chain too long or too short | Yes | Rarely |
| Float or water level set too high | Yes, in small steps | If adjustments do nothing |
| Fill valve will not shut off | Possible if you are comfortable with it | If connections are stuck or corroded |
| Supply valve will not turn, or it leaks | No | Yes |
| Water on the floor, cracked tank, or leaking base | No | Yes, and shut off the water |
| Still running after new parts | No | Yes |
Slow drains or a bowl that will not clear are a separate issue. See clogged drain: try yourself or call a plumber and the drain snake guide.
If you have a septic system
EPA septic guidance says that a single leaky or running toilet can add as much as 200 gallons of water per day, and that the more water a household conserves, the less water enters the septic system. Fix a running toilet promptly. Also keep the rest of your habits septic-friendly: the EPA says to flush only human waste and toilet paper, and to avoid chemical drain openers. See what not to flush with a septic system, and if the toilet has been running for weeks, ask about pumping and inspection in septic maintenance near me.
What not to do
- Do not leave it running. It wastes water and, on septic, loads the system.
- Do not force the supply valve. Old valves can leak or break.
- Do not use chemical drain cleaners in a toilet to fix a running problem. They do not help, and the EPA advises avoiding them on septic systems.
- Do not flush while dye is in the tank. It can stain the tank, as the EPA warns.
- Do not mix cleaning products when cleaning the tank or bowl.
What to look up where you live
- Your water utility: how to read your meter to confirm a leak, and whether it offers any leak-repair information.
- State or provincial plumbing or contractor licensing board: to confirm a plumber's licence and check complaints.
- County health department or environmental health office: if the home is on a septic system and the toilet has run for a long time.
For Canadian readers. Plumbing is regulated by each province or territory, and municipalities set their own water rules. Check your municipality and provincial regulator. Costs are in Canadian dollars and cannot be compared directly with US figures.
For plumbing company owners
A running toilet is a small job that often turns into a bigger one when the homeowner finds a leak or a worn valve, and your customers search for it by name. To be the company they find, read plumbing leads and Google reviews for plumbers, or book a call with LiveLeadsLane. LiveLeadsLane is a marketing practice for contractors, not a directory, and it does not take jobs or refer homeowners.
