A toilet that continues to run wastes water and energy, and the sound can drive you crazy. When you get tired of jiggling the handle, here’s how to fix the problem.
1] The number one cause of toilet problems is the rubber flapper at the bottom of the tank.
It can get caught on its hinge, snagged on the flush chain (which can also come loose or break), or become old and brittle and stop fitting properly. Take the cover off the tank, flush the toilet, and watch the flapper. If it’s stuck on something, unstick it; if it’s not seating well, wipe any gunk off mating surfaces, or replace it with parts from the hardware store. Ancient cottage toilets may have a teardrop-shaped tank ball instead of a flapper, with similar problems and solutions.
2] The next most likely culprit is the float.
A float that’s waterlogged or set too high will let the tank fill until water runneth over into the overflow tube. To fix, simply adjust the float level down, so that the water shuts off about an inch below the overflow opening. It seems every toilet design uses a different method to adjust the float—some have screws, others have sliding spring clips—but it’s usually easy to figure out. If the float has a leak and is full of water, stop in at the hardware store for a replacement.
3] If both float and flapper are working, that leaves only one other possibility: the fill valve.
Replacement kits are available in the plumbing section.