First, lift off the cover of the tank. Check to see if the flapper is up. The flapper is that rubber piece connected to the end of the chain that covers the valve. When you flush the toilet, the flapper lifts up, letting fresh water into the bowl. If it’s not covering the valve properly, then water will continue to run through.
The chain might be twisted. If this is the case, simply untwist the chain and the flapper will go back down. If this is a common occurrence with your toilet, you can fix the problem each time by jiggling the toilet handle after you flush. If the handle is loose, then the chain is twisted. Jiggle it until it you feel it tighten.
If the chain is not the problem, then your flapper might be damaged. This means it’s not creating a tight seal around the valve. One way to find out is to pour a little food coloring into the tank. If it seeps into the toilet bowl then you know you have a bad flapper. You’ll need to replace it.
To replace, turn off the water valve on the wall behind the toilet. Flush the toilet to empty the tank and remove the flapper. Take it with you to the hardware store to ensure you buy the right part.
The next thing to check is the float. This is the piece that moves up and down with the water level in the tank. It’s either a plastic cup around a tube or a rubber ball at the end of a metal rod. The float keeps water from running into the overflow valve. Do you see water running into that plastic vertical pipe? Then you need to lower the float.
There are two ways to do this. If the float is a rubber ball attached to a metal rod, just bend the rod down to make the ball lower. If you have a plastic cup float, look for the metal clip attached to it. You can squeeze and twist the metal clip to slide it down. Then flush the toilet and watch the water rise to make sure it works. The water level should be about one inch below the top of the overflow valve.
Ahh…do you hear that? The silence of a working toilet.