- Lift the tank lid. If water spills into the center tube, the float is set too high or the fill valve will not close. Set the float so the level stays below the top of that tube. If it still fills, replace the fill valve.
- If the level sits still and you still hear water in the bowl, the flapper is leaking. Put a little food coloring in the tank and wait fifteen minutes without flushing. Color in the bowl confirms the flapper.
- Close the shutoff on the wall, flush to empty the tank, unhook the chain, and replace the flapper with the same shape. The chain needs a little slack. Pulled tight, it holds the flapper open.
If water shows up on the floor, close the wall shutoff and stop the test. The leak may be the tank-to-bowl gasket or the seal at the base.