A running toilet is a pretty common problem and an easy fix.
A running toilet can be irritating. Not only is it very wasteful but it's pretty loud - especially at night.
There are three main components to your toilet:
the tank itself which holds the water
the float
a stop valve
After flushing, the water begins to refill the tank raising the float to a specific height allowing it to close the valve.
The most common issue for a running toilet is the misalignment of the floats arm.This allows the valve to not properly close (water keeps draining and continuous refilling) or level of water to rise too high and, therefore, trickle over into an overflow pipe and into the toilet bowl.
Fixing this misalignment issue is pretty straightforward.
remove the toilet lid
use an adjustable spanner (open-end wrench) to adjust the angle of the floats arm
it is suggested to position the float so that it closes the valve that refills the tank once the tank is little over half full (but the choice is yours)
The important thing here is to ensure the floats allows the valve to properly close the drain and to shut off the supply of water before the water reaches the level of the overflow pipe
On the off chance that you don't have any tools (the arms are normally easy to bend by hand) - however be mindful to not injure yourself or break/damage the arms.If worst comes to worst replacements parts are fairly low cost and can be purchased at your local Green Bay hardware store.