Toilet Keeps Running? Here's How to Stop It

A toilet that won't stop running is one of the most common — and most wasteful — problems in a home. The trickle you hear (or don't) can quietly send hundreds of gallons a day straight down the drain, inflating your water bill for weeks before you notice. The good news: nearly every running toilet comes down to one of three cheap, fixable parts inside the tank, and you rarely need a plumber.

Lift the tank lid and let's diagnose it.

First, run the dye test

This 15-minute test tells you whether the flapper is your culprit:

1. Put a few drops of food coloring into the tank (not the bowl).
2. Wait 15 minutes without flushing.
3. Look in the bowl. Colored water in the bowl means water is leaking past the flapper — that's your problem.

This is the same trick behind the check toilets for silent leaks maintenance task, worth doing on every toilet a couple of times a year.

Cause 1: a worn flapper (most common)

The flapper is the rubber seal at the bottom of the tank that lifts when you flush and drops to reseal. Over a few years it warps, stiffens, or builds up mineral scale and stops sealing — so water leaks into the bowl and the fill valve keeps running to replace it.

To replace it (about $5 and 15 minutes):

1. Shut off the supply valve behind the toilet and flush to empty the tank.
2. Unhook the old flapper from the overflow tube pegs and unclip the chain.
3. Snap on a matching replacement (take the old one to the store), and reconnect the chain.
4. Turn the water back on and test.

While you're there, check the chain length — it needs a little slack. Too tight and it holds the flapper open; too loose and it tangles underneath.

Cause 2: water level set too high

If you see water continuously trickling into the overflow tube (the vertical pipe in the middle of the tank), the water level is set too high. Lower it so the water stops about an inch below the top of the overflow tube:

• Modern float-cup valves: pinch the clip on the side and slide the float down.
• Older ballcock valves: turn the screw on top, or gently bend the float arm down.

Cause 3: a faulty fill valve

If the flapper is fine and the level is right but the toilet still hisses or runs, the fill valve itself isn't shutting off. Try adjusting it first; if it still won't seal, replace the whole fill-valve assembly — an inexpensive part and a straightforward DIY swap with the water shut off.

When to call a plumber

The parts above cover the vast majority of running toilets. Call a pro if:

• Water is leaking between the tank and the bowl (you'll see drips at the floor after a flush).
• The tank or bowl is cracked.
• You've replaced the flapper and fill valve and it still runs.

Why it's worth fixing today

A running toilet is pure waste — money down the drain and, on a well or septic system, extra strain on your pump and tank. Knowing where your main water shutoff and the toilet's own supply valve are makes every repair faster; see how to shut off the water to your house. For the bigger picture, the plumbing system overview covers the habits that catch silent leaks early.

Make it automatic

Build your free Owner Tools plan and we'll remind you to dye-test your toilets and inspect supply lines on schedule — so silent leaks get caught before they hit your water bill. No login, no address required.