Why Does My Toilet Run Every Few Minutes? (Phantom Flush Fix)

This is sometimes called a "phantom flush" or "ghost flush". It is worth fixing soon. EPA WaterSense says a worn flapper can make a toilet flush on its own or silently leak thousands of gallons a year (EPA WaterSense).

Graphic: summary of this guide, made by our team from the cited sources.

Confirm it in 15 minutes: the dye test

1. Take the lid off the tank and set it somewhere safe. Tank lids are heavy and break easily.
2. Put a few drops of food coloring or a dye tablet in the tank, not the bowl.
3. Do not flush. Wait.
4. Check the bowl. EPA WaterSense says that if any color shows up in the bowl after 10 minutes, you have a leak (EPA WaterSense). Portland's water bureau says to wait at least 15 minutes (Portland Water Bureau).
5. Flush afterward so the dye does not stain the bowl.

Color in the bowl means water is getting past the flapper or the flush valve. No color, but the toilet still refills by itself? Go to "Water going down the overflow tube" below.

Find which part is leaking: the pencil-mark test

Korky's test tells you whether it is the flapper or the flush valve itself (Korky):

1. Flush, let the tank refill, and mark the water level on the inside of the tank with a pencil.
2. Turn off the supply valve behind the toilet and wait at least 25 minutes.
3. If the level drops below the mark, something in the tank is leaking.
4. Leave the water off for a couple of hours. If the level stops at the flapper or flush seal, replace the flapper or seal. If it drops to a point on the overflow tube or the bottom of the tank, the flush valve needs replacing.

The causes, in the order to check them

1. The chain is too short, too long or snagging

A chain with no slack holds the flapper slightly open. A chain that is too long can fold under the flapper. Kohler says the chain should have roughly one to two links of slack at most (Kohler). Also check that the handle arm is not rubbing the tank lid or catching on anything.

2. A worn, warped or dirty flapper

Rubber flappers stiffen and warp with age and chlorine. Portland's water bureau says that if you gently rub the flapper and get streaks on your fingers, you should replace it right away (Portland Water Bureau). The NYC Department of Environmental Protection adds that in-tank cleaning tablets can corrode the flapper and other rubber parts (NYC DEP). EPA WaterSense recommends replacing the flapper at least once every five years (EPA WaterSense).

Buying tip from EPA WaterSense: take the old flapper, or a photo of it, to the store, and note its width and whether it has a float that may also need replacing.

3. A rough or damaged flush valve seat

The flapper seals against a ring at the bottom of the tank. Grit and mineral buildup can nick it so even a new flapper cannot seal. NYC DEP lists grit and sediment damage to the flush valve as a cause of this kind of leak. Gently clean the ring with a soft scrub pad. If it is cracked or pitted, the flush valve needs to be replaced.

4. Water going down the overflow tube

If the dye test was clean but the toilet keeps refilling, look at the overflow tube (the open pipe in the middle of the tank). If water trickles into it, the tank is filling too high, or the fill valve is not shutting off. Portland says the correct water level is about 1/2 to 1 inch below the top of the overflow tube, and explains how to adjust the float on both float-ball and vertical-float fill valves (Portland Water Bureau). Kohler lists overfilling into the overflow as one cause of occasional running.

If adjusting the float does not stop it, the fill valve is worn or clogged. Korky says adjusting, cleaning or replacing the fill valve fixes a toilet that keeps running after the tank is full (Korky). A fill valve that sticks open matters: NYC DEP says water can flow through an open fill valve at three to five gallons per minute, up to 4,000 gallons a day.

Only runs at night?

If the toilet behaves during the day but you hear it refill overnight, check the water level first thing in the morning. Santa Barbara's water department says many toilets leak overnight when water pressure rises, pushing the tank level above the overflow tube (City of Santa Barbara). Lower the float a little more than seems necessary and check again the next morning.

A "universal" flapper that isn't

If you already replaced the flapper and the toilet still wastes water, watch a flush with the lid off. Santa Barbara says the flapper should close after a few seconds with about 2 inches of water still in the tank; if it stays open longer, refill water runs straight down the drain, a sign of a mismatched flapper (City of Santa Barbara). Buy the flapper made for your toilet's brand and model (the model number is usually stamped inside the tank).

Replacing a flapper: what "done" looks like

Most flappers clip onto two pegs on the sides of the overflow tube, or slide over the tube with a ring.

1. Turn off the supply valve behind the toilet and flush to empty the tank.
2. Unhook the chain from the handle arm and unclip the old flapper.
3. Clean the flush valve seat.
4. Fit the new flapper and attach the chain with about one to two links of slack (Kohler).
5. Turn the water back on, let the tank fill, and flush a few times to make sure it closes every time.
6. Repeat the dye test. If no color reaches the bowl, the fix worked.

Toilets without a tank

Some homes and many apartment buildings have tankless toilets with a flush valve on a pipe from the wall. NYC DEP says that if water keeps moving in the bowl after a flush, the valve is leaking, and that phantom flushes on these toilets can come from pressure changes in the building and should be checked by a licensed plumber (NYC DEP).

When to call a plumber

• The supply valve behind the toilet will not shut off, or it leaks when you turn it.
• The flush valve needs replacing and you are not comfortable removing the tank from the bowl.
• The toilet still runs after a new flapper and fill valve adjustment.
• Water is leaking onto the floor rather than into the bowl.