Toilet tank not filling up with enough water

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

Keep in mind that if you limit the amount of water too much, the 3.5 gallon toilet will not flush properly.

This looks like an old Kohler Rialto toilet. The proper way to adjust the water level is to tighten down on the adjustment screw located on the very top of the fill valve. The fill valve is the the piece that the float ball screws into on the left side of the tank.
Tighten the screw down and flush the toilet. Wait for it to refill, and check the level. If you need less water, tighten again, let fill and check level.
There are also two old school methods to save water in your toilet. One is to put one or two bricks into your toilet tank. This reduces the amount of water that fills the tank. The second method is if the fill valve has a float ball on a metal rod, you can bend this rod down into the water. This makes the fill valve shut sooner. Don't bend too far or too fast because the chlorine in the water weakens the brass rod that the float ball attaches to.

After flushing the toilet, water still fills the tank till then the shuts off valve reaches a certain level. When the shuts off valve reach the level it disconnect the water connection to the tank and the filling process of the tank shuts off.

So, if your fill valve didn't shut off then maybe there's a problem with the shuts off valve, open the fill valve and fix it. If you can't fix it call a plumber for it.

There is a problem with your fill valve. The fill valve has a float connected to it, that rises up as the water level reaches its correct level, which then shuts off the water entering the tank.
Replace the fill valve. They run in the neighborhood of $10-15.

1.) Check to make sure that the water shut-off valve is all the way open (the water valve a.k.a. the shut-off valve is located behind the toilet near the wall or the floor, depending upon installation placement.) The water supply line attaches to it and feeds up into the refill valve assembly inside the toilet tank.
2.) Check the float assembly or the refill valve assembly, make sure it hasn't bound up by getting caught on another part inside the tank.
3.) Check the water level to make sure that it sits about 1 inch below the overflow tube in the middle of the tank. If the water is lower, adjust the float inside the tank to raise the water level. For models that have a ball float, turn the screw on top of the fill valve clockwise to raise the water level. For models that contain a cylinder float valve attached to the fill valve, squeeze the clip on the side of the float and pull the float up until the water reaches the desired level.

If you have a supply shut off to fixture shut it off and disconnect supply line from inlet to toilet . If your supply line to toilet is a flexible line then bend it so that you can direct water to small container. Slowly turn valve on to see what flow rate is at that point. If flow rate is not good then I would shut water off to house and replace valve. If flow rate to toliet is good I would reccomend you replace flush vallve. To do this shut off water supply to toilet. Disconnect supply nut to bottom of flush valve. There will be a retaining nut that holds flush valve in place in toilet tank. Remove flush valve after removing fill tube from flush valve to overflow tube. Replace with toto replacement valve or use Fluidmaster 400A. Instructions on box of 400A are easy to follow and if you have flex connector you won't need supply line washer. I would reccomend that before you install new valve that you put rubber gasket on shank of valve and slid it about halfway up the shaft. Make sure that inside of tank is dry and use a small bead of silicon caulking on top and bottom side of shaft gasket. slid gasket the rest of the way on valve shank,install in tank and put on retaing nut hand tight. Push down on top of valve and using channel lock pliers finish tightening nut securely.You may need to reach into tank and grasp valve body to stop it from turning. There are other things you can do if you have a working supply valve. Shut off valve and remove screws that hold top of valve in place and remove and clean surfaces. You can turn valve on slowly to help flush out any rust or mineral deposits. I hope this is of some help to you. Thanks

The ball float follows the tank water level, and repeated cycles of the float dropping and opening the fill valve would likely reflect a leak in the flush valve. You could try adjusting the float arm downward so that it will respond to a lower water level. Try turning off the supply valve, flushing it and listen for water leaking past the flush valve after it closes. If it does, replace the flapper or adjust the chain.

You don't have to replace, You just need to adjust the fill valve. If you have the ball **** type just tight the top phillips screw. If you have the newer type, close the water valve under the tank and Push down a plastic ring at the bottom of the filling valve, Push down the top of the valve, lift the plastic ring to it's place and open the water valve.

shut the water off to the toilet .Remove the toilet supply from the tank end.slowly turn the valve on to see if their is any water coming thru the supply.If water is coming thru the supply than you know you need to change the ballcock.This is the part in the tank where the water comes out of.

Chances are the flapper is leaking. Thats causing the random refilling as the tank slowly loses water into the bowl.
Replace the flapper with only the best available at your supply house. the cheap ones tend to leak even when new. The good ones are less than 8 bucks most places.

If your fill valve has the float ball, there should be a screw right on top of the fill valve at the end of the rod holding the ball to adjust the water level.
Closckwise lowers the level.

Be carefull not to break the plastic ones. If the adjustment is all the way in or does not work, you will need to replace the fill valve.

You could also try bending the metal rod holding the ball, but only as a last resort.