Home / Common plumbing problems / Toilet keeps running
Plumbing problem
Why does my toilet keep running?
The short answer
Fluidmaster’s troubleshooting starts by sorting a running toilet into one of two parts. Either the flapper is letting water leak from the tank into the bowl, or the fill valve is letting the tank fill so high that water spills into the overflow tube. Fluidmaster, which makes both parts, calls the flapper the most common problem (Fluidmaster), and EPA WaterSense says most toilet leaks come from old or worn-out flappers (EPA WaterSense).
What people usually report
The sound of water running long after a flush, a tank that refills for a few seconds when no one has used it, a handle that has to be jiggled, or a faint trickle visible in the bowl. Sometimes the first sign is a water bill that jumped.
What the sources say the causes can include
- A worn flapper. EPA says an old or worn flapper can cause the toilet to flush on its own or silently leak thousands of gallons a year, and recommends checking it periodically and replacing it at least every five years (U.S. EPA WaterSense).
- A fill valve set too high or fouled with debris. If the water rises high enough to drain into the overflow pipe, Fluidmaster points to the fill valve, where dirt and debris can lodge (Fluidmaster (toilet fill valve and flapper manufacturer)).
How to find out
- EPA’s dye test. Put a few drops of food coloring in the tank. If color shows up in the bowl after 10 minutes without a flush, the toilet is leaking (U.S. EPA WaterSense).
- Watch the overflow tube. Turn the water supply back on and look inside the tank. If the water rises high enough to drain into the overflow pipe, the fill valve is the issue (Fluidmaster (toilet fill valve and flapper manufacturer)).
- Mark the water line. With the tank full, turn off the water to the toilet, mark the level, and wait 10 to 15 minutes. If it drops, Fluidmaster says to replace the flapper first (Fluidmaster (toilet fill valve and flapper manufacturer)).
Why it is worth fixing soon
EPA WaterSense says household leaks can waste 180 gallons a week in an average family, or 9,400 gallons a year (U.S. EPA WaterSense), and that toilets are often the culprit (U.S. EPA WaterSense). Toilets already account for nearly 30 percent of an average home’s indoor water use (U.S. EPA WaterSense). If the toilet itself is old, WaterSense-labeled models use 1.28 gallons per flush or less, compared with as much as 6 gallons for older ones (U.S. EPA WaterSense).
Both fixes are parts repairs rather than a new toilet. If you are weighing replacement anyway, see toilet installation cost. If the bill is high and the toilet passes the dye test, see high water bill with no visible leak.
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Try this while you wait: screening tools
The dye test confirms a leak. These are the parts and test tablets people look for once they know which part is at fault. Check your toilet’s brand and flush valve size before you buy, or leave it to a licensed plumber.
- Toilet leak detection dye tablets on Amazon →The same check as EPA’s food-coloring test.
- Toilet flappers on Amazon →Flappers come in more than one size; match it to your flush valve.
- Toilet fill valves on Amazon →For a tank that fills into the overflow tube.
As an Amazon Associate we earn from qualifying purchases. Buying through these links never changes your price. We have not tested these products, and the links open an Amazon search, not a single recommended item.
Local help
Who to contact
If you are on a public water system, your water utility is the first call for anything that affects the water itself. Its phone number is on your bill and in its annual water quality report.
For work on the pipes and fixtures inside your home, hire a licensed plumber and confirm the license before work starts. Our guide to choosing a plumber covers what to ask. License lookups for the areas our city pages cover:
- FL: Florida Department of Business and Professional Regulation (DBPR)
- IA: Iowa Plumbing and Mechanical Systems Board (PMSB), administered by Iowa DIAL
- MO: Kansas City, MO City Planning & Development (plumbing license, city-issued)
- NE: City of Omaha Building and Development Division (plumbing license, city-issued; Nebraska has no statewide plumbing board)
- NV: Nevada State Contractors Board (NSCB), Classification C (plumbing)
- OK: Oklahoma Construction Industries Board (CIB)
- TX: Texas State Board of Plumbing Examiners (TSBPE)
Elsewhere, search your state’s plumbing or contractor licensing board. Some cities issue plumbing licenses themselves.
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Common questions
Running toilet questions
What is the most common cause of a toilet that keeps running?
Fluidmaster, which makes toilet fill valves and flappers, calls the flapper the most common problem. EPA WaterSense agrees that most toilet leaks are due to old or worn-out flappers. The other common cause is a fill valve that lets the water rise high enough to drain into the overflow tube.
What happens if I ignore a running toilet?
EPA WaterSense says an old or worn flapper can silently leak thousands of gallons a year, and that household leaks in an average family can waste 180 gallons a week, or 9,400 gallons a year. Toilets are often the culprit. That water shows up on the bill.
Is it normal for a toilet to randomly run for a few seconds?
EPA WaterSense says an old or worn flapper can cause a toilet to flush on its own. A tank that refills briefly when nobody used it is a sign water is slipping past the flapper. EPA’s food-coloring test confirms it.
Why is water constantly trickling into my toilet bowl?
Water reaches the bowl two ways when nobody flushes: past a flapper that does not seal, or over the top of the overflow tube when the fill valve lets the tank fill too high. Fluidmaster’s two checks tell you which: watch whether the water line reaches the overflow tube, and mark the water line with the supply off to see whether it drops.
Sources and limits
- Fluidmaster (toilet fill valve and flapper manufacturer), How to Fix a Running Toilet. Checked 2026-10-05.
- U.S. EPA WaterSense, Fix a Leak Week. Checked 2026-10-05.
- U.S. EPA WaterSense, Statistics and Facts. Checked 2026-10-05.
- U.S. EPA WaterSense, Residential Toilets. Checked 2026-10-05.
This page summarizes guidance published by the agencies and organizations listed above. It is general information, not a diagnosis of your home or your water. Guidance can change, so check the linked source, your water utility, or your local health department before acting on it. PlumbingRepairCost is not affiliated with any agency named here. Spotted an error? Email hello@plumbingrepaircost.com and we will check it against the source.