A toilet does not flush by itself, even though your toilet makes flushing noises when nobody is in the bathroom at the time. A mechanical condition with a toilet will cause it to sound as if it is being flushed by an unseen force. Once you understand what causes the problem you will be equipped to provide a solution.
When your toilet sounds like it randomly flushes, even though nobody is near the toilet, it is referred to as phantom flushing. Despite the name, when a toilet phantom flushes it does not actually flush. The sound you hear that sounds like flushing is the tank refilling water that has been lost, which you hear after you flush a toilet. A leak in the toilet's tank, not paranormal events in your house, causes phantom flushing.
While phantom flushing may scare you as you are startled by the sudden sound, or it annoys you as you continually hear the noise of the toilet's tank refilling, even more importantly, the phantom flushing toilet wastes water. The constantly refilling toilet tank will lead to a higher water bill as your household water usage increases. How often the phantom flushing occurs affects how much it will raise your water bill.
Detecting the Source
Before you can fix a phantom flusher, you must first determine the source of the leaking water. You need to remove the toilet tank's cover and gently place it aside. Once the toilet is idle and not making any noise, drop in a few droplets of food coloring into the tank's water. The key is to use a dark food coloring that is easy to see in the water. Several moments of waiting and watching will show you where the water is leaking out of the tank, since the food coloring will be pulled to the site of the leak.
Fixing the Problem
One of the most common causes of phantom flushing is a worn-out flapper valve in the toilet's tank. Replacing the flapper involves removing the old flapper and installing a new one. You must also adjust the flapper's chain so it allows the flapper to sit down securely over the drain opening, but the chain is not so long that it binds up. If you find that that water is leaking out at another point, such as the bolts in the bottom of the tank, tighten the part where the leak is occurring or replace the parts.