A toilet that spontaneously needs to refill the tank when it hasn't been flushed or that runs an excessive amount of time after use is showing signs of mineral buildup in the fill valve. Save water and save on the cost of a professional plumber by trying a little bit of sediment removal yourself. A routine cleaning of the toilet fill valve can have it running smoothly again in no time.
Shut off the water supply to the toilet. Remove the tank lid and locate the toilet fill valve. Remove any screws on top of the fill valve and set aside. This will allow you to remove the fill cap for the valve.
Cup your hand over the exposed valve and slowly turn on the water. Proper positioning of your hand will keep you from being sprayed with water.
Allow water to flow freely out of the valve. This will flush any debris from the fill valve line. Shut off the water after a few seconds.
Turn over the fill cap and locate the fill valve washer. It can be removed by gently prying with a standard head screwdriver. Remove any obvious mineral buildup by rubbing gently with your fingers. Inspect for cracks or wear. Replace if needed.
Return fill cap to valve and secure with screws. Replace tank lid and turn water back on.