You are in another room, nobody has touched the toilet, and you hear it refill for a few seconds. Plumbers call this a phantom flush. It means water is slowly escaping from the tank into the bowl. When the level drops far enough, the fill valve opens to top it back up. The toilet is not haunted, but it can waste a surprising amount of water.
Find the Cause With Food Coloring
Take the tank lid off and add ten drops of food coloring to the tank water. Do not flush. Wait twenty to thirty minutes. If color shows up in the bowl, water is leaking past the flapper or the flush valve seal. If the bowl stays clear, look at the fill valve and the overflow tube instead.
Cause 1: A Worn or Warped Flapper
This is the most common cause. The rubber flapper at the bottom of the tank hardens and warps over time, especially with chlorinated city water, and stops sealing.
- Turn off the shutoff valve and flush to drain the tank.
- Unhook the chain and pop the flapper ears off the pegs on the overflow tube.
- Take the old flapper to the store, or note the brand and the drain opening size, usually 2 or 3 inches.
- Install the new flapper and set the chain with about half an inch of slack when the flapper is closed.
While the tank is empty, run a finger around the drain opening the flapper sits on. Mineral buildup or a rough spot can keep even a new flapper from sealing. Sacramento water is moderately hard, and scale on the seat is common in older toilets. A light scrub with a nonabrasive pad usually clears it.
Cause 2: A Chain That Is Too Tight or Too Long
A chain with no slack holds the flapper slightly open. A chain that is too long can get trapped under the flapper. Either way, water leaks into the bowl. Adjust the clip so the chain hangs with a small curve.
Cause 3: The Water Level Is Set Too High
If the bowl stayed clear in the dye test, look at the overflow tube in the center of the tank. When the water level sits above the top of that tube, water spills down it into the bowl and the fill valve keeps cycling. The water line should sit about an inch below the top of the overflow tube. Lower it by turning the adjustment screw or sliding the float clip on the fill valve.
Cause 4: The Refill Tube Is Pushed Too Far Down
The small flexible tube from the fill valve should clip onto the top of the overflow tube, not reach down inside it. If it hangs below the water line, it can siphon water out of the tank. Clip it so the end sits above the water.
Cause 5: A Failing Fill Valve
If the toilet hisses, refills slowly, or keeps running long after the tank is full, the fill valve is worn. Replacing it is a bit more work than a flapper but still a common repair. Fill valves and flappers are inexpensive, and if the toilet is old, replacing both at once saves a second trip.
When to Call a Plumber
Call us if the tank or the bowl is cracked, the tank bolts are rusted and dripping, the shutoff valve will not close, or the toilet still runs after a new flapper and fill valve. At that point the problem is the flush valve seal under the tank or the toilet itself, and a replacement often makes more sense. See our toilet installation and repair service.
Running Toilet Questions, Straight Answers
Does a toilet that runs by itself waste a lot of water?
Yes, it can. A slow flapper leak loses a little water every cycle, all day and all night. A badly leaking flapper can add hundreds of gallons a day, which often shows up first as a jump in the water bill.
Can I use a universal flapper?
Yes, for many toilets. Check the size of the drain opening first. Some newer toilets use a canister or tower flush valve instead of a flapper and need the matching seal from the manufacturer.
Why did a new flapper not fix the problem?
Usually the valve seat is rough or scaled, the chain is adjusted wrong, or the flapper is the wrong size. If the dye test still shows a leak after all three are checked, the flush valve seal under the tank may have failed.
Related Guides
Need a Hand?
A short video of the inside of the tank is often enough for us to tell you what part you need. See our toilet installation and repair service.
