Fixing a toilet that runs or refills by itself

Confirm the leak

Add a few drops of food coloring to the tank, not the bowl, and wait 10 minutes without flushing. If color appears in the bowl, water is leaking past the flapper. Flush afterward so the dye does not stain. If you hear the toilet refill every so often with nobody using it, that is the same leak.

The three usual causes

• The flapper. The rubber seal at the bottom of the tank wears out. The EPA recommends checking it periodically and replacing it at least every five years. Take the old one, or a photo of it, to the hardware store; flappers come in 2- and 3-inch sizes.
• The chain. Too tight and the flapper cannot seal; too loose and it can get caught under the flapper. Leave a little slack.
• The fill valve and water level. If water is running into the overflow tube, the fill valve is set too high or not shutting off. Adjust the float so the water stops about an inch below the top of the overflow tube, or replace the fill valve.

How to change a flapper

1. Turn off the supply valve behind the toilet and flush to empty the tank.
2. Unhook the chain and slide the old flapper off its pegs.
3. Fit the new one, reattach the chain with a little slack, and turn the water back on.
4. Repeat the dye test.

If the shutoff valve behind the toilet will not turn or leaks when you touch it, stop and call a plumber; old valves often fail when moved.

Other toilet problems

• Water on the floor at the base: usually a failed wax ring. The toilet has to come up; do not just caulk around it.
• Rocking toilet: loose closet bolts or a damaged flange; fix it before it breaks the wax seal.
• Weak flush: clogged rim holes or a partial blockage.

Replace the toilet?

Toilets made before the mid-1990s can use far more water per flush than current models. EPA WaterSense labeled toilets use 1.28 gallons per flush or less. If an old toilet keeps needing parts, a new one may cost less over time.