The float goes under the flapper which stops the tank from filling up with water, the water keeps running back out.How do I know that the float is set in the right spot.

hi Patricia.
Overview Toilets haven't changed much in the last 80 years. After a flush, water still fills a tank, lifting a float that shuts off the water when it reaches a certain level. A lever still opens a flapper to cause the flush, falling back into place when the water level drops. So it's no surprise (nor any consolation) that we face the same flush problems today that our grandparents did. Sometimes the flush is too wimpy, sometimes the toilet keeps running, and sometimes the bowl doesn't refill.
Our ace plumbing consultant has a simple four-step strategy to solve 95 percent of these problems. You can complete the first three steps in five minutes. That'll solve most problems. The fourth step is usually easy too, but not always. More on this later. These steps work for most toilets but not for pressure-assist models.
Check the fill tube

Overflow tube problem

Push the fill tube firmly onto the fill valve. Make sure the fill tube sends water into the overflow tube.Remove the tank lid and find the fill tube. It's a small flexible tube that runs from the fill valve to the overflow tube. While the tank refills, this tube squirts enough water down the overflow tube to refill the bowl after the completed flush. If this tube falls off or the water stream misses the overflow tube, the bowl won't fill and your next flush will be wimpy (that is, won't develop a strong siphon). Reattach the fill tube and make sure it perches about 1 in. above the rim of the overflow tube. Flush the toilet and watch the water stream to make sure it goes down the overflow tube.
Adjust the fill height

Check the float

Adjust the float to set the water level. Pinch the clip and slide the float up or down on the rod. Keep adjusting the float until the water shuts off at the proper level.The water level in the tank is controlled by an adjustable float. A float that's set too low produces a weak flush; if it's set too high, water spills into the overflow tube and the fill valve won't shut off. The toilet keeps running. Look for the fill level mark on the inside back of the tank and mark it on the overflow tube so you can see it more easily. If you can't find it, measure down about 1 in. on the overflow tube and make a mark. Then flush the toilet and see if the water reaches and stops at that mark. If not and the toilet keeps running, adjust the float up or down. If you have an old toilet, you'll have to bend the brass rod that connects to the float ball to make adjustments. But with newer toilets you usually turn a screw or slide a clip along a rod. Flush the toilet after each adjustment.
Also make sure that the water level is at least an inch below the C-L (critical level) marked on the fill valve. You can adjust the height of many valves to raise or lower the C-L.
Occasionally the fill valve simply won't shut off, which means that it's defective. If so, turn the water supply off at the shutoff under the tank. Buy a replacement valve (sold at hardware stores and home centers). You don't have to match the old one; many, like the one shown, fit most toilets. It's a 15-minute change-out.
Adjust the flush handle/flapper chain

Flapper chain fix

Adjust the chain to leave a little slack with the flapper closed. Then cut off the excess, leaving about an inch.A chain that's too short or tangled won't allow the flapper to close and water will continue to leak into the bowl. This causes the fill valve to cycle on and off to refill the tank. A chain that's too long, or a flush rod that hits the the tank lid, won't open the flapper wide enough to stay open for the full flush. You'll find yourself having to hold the lever to complete a good flush.
To avoid these problems, adjust the linkage in the chain to leave only a slight bit of slack when closed. Cut the chain at the rod to leave only about an inch extra to reduce the potential for tangles. Then put the tank lid back on and make sure the flush rod doesn't strike the lid when you press the lever. If it does, bend it down slightly and readjust the chain.
Replace the flapper

Change the flapper

Unsnap the old flapper and take it with you to the store to find an exact replacement. In addition to the closest replacement, pick up a "universal" type.If you've completed the first three steps and your toilet keeps running, chances are you have a worn-out flapper. Turn off the water, remove the old flapper and take it to the store to find an exact replacement. (Hardware stores often carry a wide variety.) Most flappers snap over ears on the overflow tube. Others have a ring that slips over the tube.
Now here's the catch. You may not find an exact match. The range of flapper styles has mushroomed over the last 15 years, and you may find 15 to 20 flapper options on the store shelf. Some packages include specific brand and model information (so note yours before you leave home). Others have a "universal" label. If you can't find an exact replacement, try the closest one and pick up a universal type as well. They're cheap, and the extra one just might save you a second trip to the store! (Avoid the "adjustable" types unless you're replacing an adjustable one.)
Install the new flapper and make sure it opens and closes freely. Then test it. If the toilet keeps running or runs intermittently, you're not getting a good seal. Try a different flapper if the toilet won't stop running.
If you just can't find a flapper that seals, consider replacing the entire overflow tube/flapper. On most toilets (two-piece), this means removing the tank. It's not difficult and you don't need special tools. It'll take you about an hour, and you'll avoid that expensive plumber service call.
if you go to this link it will show you step by step on how to fix it. How to Stop Running Toilet Family Handyman

the fill valve is not letting water in you either have a float that raises up when water is full so when you flush the float drops down letting water in then when water raises it shuts off i would replace the float fill valve and corky flapper.... here is what you do .... first shut water off where it goes up to the tank....... flush commode to empty as much water from tank....... reach up under tank there is a plastic coupling that connects the water supply line to the bottom of the toilet tank...put a small pan under the shut off valve that goes to the toilet some water is going to drain from the tank when you take the coupling loose..... turn the coupling counter clockwise ( use a channel lock adjustable wrench to loosten then had turn) once this is loose you can pull the riser tube away from the tank...... now there is a plastic nut that screws the shaft to the bottom of the tank loosten with channel lock then remove with hand by turning counter clock wise ( you will get a bunch of water flowing down to the pan) remove the entire fill valve , replace with a fluidmaster fill valve ( about 8 bucks from big box store when you take the new fill valve out of the box there is a neopreme seal you must put on the new threaded shaft ( it has an inner ring you may have to punch out) once you put this on you can insert the entire shaft down through the hole in tank then secure with thin nut provided tighten but do not overtighten then put coupling back on,,,,,put the over flow tube on the tit of the fill valve and stick down into over flow ok thats done when you go to big box store purchas a 5 buck corky flapper (red caus it can handle chlorine water better) remove the old one at bottom of tank( just two clips to remove and chain attached to flush lever...install new one be shure chain does not have a lot of slack so it does not fall under flapper seal when you flush......OK YOU ARE DONE TURN WATER ON WATCH TANK FILL LOOK FOR LEAKS TAKE A TOWEL AND DRY ALL AREAS THEN TAKE YOUR HAND AND FEEL FOR LEAKS UNDER TANK AND DOWN TO SHUT OFF VALVE .....CONGRATS YOU DID IT!

Yes it could be valve just cause you changed the flapper doesnt mean that you stop water from filling in tank the valve that shuts water of can still be running the water will go down the bowl fill tube that is were the black tube goes that connects to the top of white pipe the simple whey to find out is just push down on black float and water will stop add in tank let off black ball and water should stop or just lift up on float arm and water should stop bend float arm if necessary.

Water is either running (1) into the overflow tube or (2) out to the toilet under the flapper at the bottom of the tank. If (1) lower the ball or float. Done differently depending on model. If (2) replace the flapper with new flapper designed for your model. (Note: Raise manually the float valve and if water still runs out the little tube that goes into the overflow tube then fill valve is defective. Replace it.)

Hi turtlerose07...

Sounds like you have one or two problems with the fluidmaster 400.
1...The float is set too high allowing the water to overflow into the overflow pipe and allowing your pump to run too much.
2...Flapper valve inside at the bottom of the tank is not sealing properly, thus allowing water to leak and causing the fluidmaster to keep trying to fill the tank with water and causing the pump to run too much.
Please take time to rate me

The Kohler Cimarron is one of the most popular and reliable toilets out there. (My Favorite). However, depending on the hardness of the water and if you use cleaner tabs in the tank, these factors can lead to a malfunction.
The first thing you should do is hold the flapper (rubber seal inside the tank that releases the water down to the bowl) down with your hands for a few seconds after a flush and see if the toilet stops running. Sometimes the flapper doesn't seal properly therefore the fill valve keeps working non stop. Stopping the fill while holding the flapper down will confirm that your flapper needs to be changed.
If this doesn't work then try this....
The other common problem with a running toilet is with the fill valve itself. There is an attached float on the fill valve that goes up and down depending on the water level. Once the water level rises, it rises the float, and the float tells the fill valve to stop filling the tank. While the toilet is running (hissing), try raising the float all the way up with your hand and see if it stops. If it stops but not consistently with every attempt, then you will need to change the fill valve. I believe the Fluidmaster 400A is the replacement model.

if you can see the water running in the bowl it's a good chance that the flappers warn http://www.aplumbers.com/residential/toilet
1. tank the tank lid off.2. flush the rubber thing that comes up and allows the water to go to the bowl is the flapper 3. remove 4. replace that should fix it.
problem 2
1. tank tank lid off.2. if the waters flowing over the long tube in the center and down then the water level is too high3. adjust the level either it will have a ball **** or a float in either case   a ball **** adjusts by a screw on the fill valve. the float has a either a metal rod w/ a pinch clamp or a plastic long screw type thing.4. adjust water level .5. barely lift handle to allow a little water out til fill valve kicks on then release handle til valve stops .6. just keep re adjusting til you get the water level right there should be a molded in line for the level on the back of the tank.

It's possible there's too much tension on the chain which won't allow the flapper to completely seal and let the tank fill. If this is not the case, the float may be stuck. If the float is sticking you're better off replacting it. If the tank is filling and water is overflowing into the tube, then it's the float.

the flapper is not closing all the way in the tank. if, when the handle is at rest, the flapper chain is too taut, the flapper is not closing all the way. so loosen the chain. if there is slack, the flapper is not making a good seal and is letting water through. or if in the tank the water is going over the standing up overflow tube, you need to adjust the float. if you have the ball float, lift it up slowly and see if the water stops running. if not, replace the ballcock (valve where the float is attached. if it does stop, unscrew the ball a little or bend the ball arm down a bit until the water stops short of the overflow. if you have the shuttle float, do the same test. if the water does shut off, adjust the shuttle accordingly.

Hi,

If the flapper base has a nick or debris on the lip of it, water can get by, dropping the level. You might also check the tube attached ti the flapper; if it is cracked, water will also escape through there. Make sure that the water level is not too high above the fill line. If it is, it will overflow the same tube attached do the flapper base.
Less frequently, but a possibility is the adjustment of the chain or flapper float. If the chain is left too long, it can get under the edge of the flapper and keep it from sealing. That's why I like the tupe with a small float attached to the chain. If the chain is too short going to the handle, the flapper may not seat fully. If the flapper chain has a float assist attached to it, the float can sometimes catch on other things in the tank, most noticeably the float lever, if equipped. Speaking of which; if you installed the fill valve type that has a ball float on it, the ball can rub against the side of the tank, the overflow tube, or catch the flapper chain/handle/flapper float. The correction cor this is to reposition the fill valve assembly so the ball has good range of motion.
If all else fails, you can replace the entire tank and guts for about $30. I recently did this for a cracked tank, and got one at Lowe's. It was a generic, and went on an American Standard. Worked fine.

Pull the lid off of the tank and just look for the obvious!

Best regards, --W/D---