A toilet that runs constantly can cost you hundreds of dollars in water bills from the city if you let it run for several hours or wait for a plumber. You can fix a few of the things that cause a toilet to run like that. In most cases, it won’t cost you much, if anything, to fix these issues.
Toilets are uniquely designed and engineered so that each component in the tank operates in tandem with the next. When one component is broken or not working as expected, that is when you get a running toilet problem. Start by lifting the lid off the tank and taking a look inside. Everything should be attached to something else. Anything that is not attached, broken, or hanging loose is the culprit.
There should be a small metal chain that connects the flush handle inside the tank to the flapper. The flapper is the rubber stopper at the bottom of the tank. When you push the handle down, the chain connected to the top of the flapper pulls up on the flapper. When the chain is disconnected, the flapper may not float down and reseal properly.
Water continues to rush out of the hole under the flapper creating the running toilet scenario. Reconnect the chain. You can shorten or lengthen the chain as needed with something as simple as a paper clip.
The fill valve is activated when the float (i.e., the black rubber ball thing on the end of an arm) drops to lift open the fill valve. If the float isn’t connected to the fill valve, water will keep running into the bowl and the tank can’t refill. The toilet will keep trying to fill the tank unsuccessfully, but without the float to resurface to the top of a filled tank, it won’t stop. Look for the disconnection and reconnect it.
There’s a tube that runs down to the bottom of the tank that takes in water from the hose under the tank connected to plumbing in the wall. The fill tube connects to the fill valve to fill the cylinder and fill the tank. If the tube is disconnected, the tank continues to run and fill. Reconnect it.