To best answer your question - It would be best to go over some basics, so you can determine for yourself what the actual problem is. There can be several things that are causing the problem and with a little information you can eliminate what isn’t YOUR particular problem/
Consider first the three culprits that usually cause a toilet to constantly run. First: You have a supply line to the toilet that supplies all water The amount of the water going into the toilet is controlled by the float inside the tank. (remove the lid and look inside the tank -see the large round float? Some tank shutoffs are different but most have the float.) When the tank fills the float rises and when it reaches the proper amount of water level; to properly flush your particular toilet, it shuts off water coming in from the supply line. Also if the float rod is bent or hanging up on the side of the tank it can not rise and cause overrunning. Or if it is corroded, caked up with sediment, (iron, magnesium, calcium, etc) it can cause blockage and not allow the float to shut off the water… Also look for a stand pipe that has a small tube running to it, and see if water is running to it when the float is in the full tank position.
Now, before you do anything else, Reach in and GENTLY pull on the chain that drops to the flapper. See if you can tell if water is seeping around the flapper (by listening closely) It can also help if you have some food coloring and you put some in the tank to watch for color in the bowl as you try the proceeding tests.
THOSE are the three items that mostly cause toilets to run constantly.
Sometimes - it is as simple as CAREFULLY bending the float downward so that the float will come to the top sooner and cause more pressure to be applied to stop the incoming water. These get ‘monkey-ed up’ when people put blue water tablets, hang chlorine baskets, or even put bricks in the tank to save water! That usually knocks the float around. If you have the food coloring in the tank green or yellow works best! You should be able to see any that flows into the bowl.
OK, if you shut off the supply of water and water is still being released into the bowl (without flushing!) Flush it, reach in and lift the flapper. Run your finger around the pipe that faces upward (about two inches in diameter) Don’t worry about putting your hand in the TANK part of your toilet, the black, or red sludge won’t hurt you! If you feel anything such as a groove or a nick, or crusted scale, this could be what is not allowing the flapper to seat properly.
If the flapper seat is OK, then check the bottom of the flapper that sets on the seat. Is it clean? can you clean it? If the rubber is good, try using your fingernail to scrape it. Also check for any cracking in the rubber -or worn spots. After checking this and cleaning the flapper and its seat, refill the tank and see if it stopped the running. Use more food coloring as the tank fills and watch carefully to see if there is any color in the bowl. THERE SHOULD BE NO COLORING SEEPING INTO THE BOWL -AT THIS POINT. IF THE FLAPPER AND SEAL ARE WORKING.
If there is NO coloring getting to the bowl and the toilet stops running at this point -YOU solved it!
If the water is still not shutting off and the water is coming into the tank but going down the overflow tube (at the top of the water level) AND the float is up -most likely the filler stand-pipe is bad and needs replacing. (NOT a major expense) If you can remove it, do so, and take it with you in a plastic bag to a plumbing parts, HD, Lowes, or local hardware and show them what you need. It’s a simple process, and if you take your time, read the directions, and GENTLY loosen the nuts, and remove the supply hose, (after the water is OFF) you should be good to go!
Good Luck, and if you can’t remember ‘Lefty Lucy -Righty Tighty” -call a plumber!
