Toilet Tank Not Filling But Water Running Troubleshooting (8 Issues Fixed!)

A toilet tank not filling but water running is a problem that can interfere with the toilet’s flushing. When you flush a perfectly functional toilet, water should flow from the tank into the bowl while the tank refills to its predetermined level, and anything short of that signifies a problem.

Your toilet tank isn’t filling but the water keeps running because of a leaking flapper, the wrong height of the float, a faulty fill valve, and a cracked overflow tube. Water supply line issues, low water pressure in the toilet tank, and trip assembly problems also contribute to the problem.

You can fix most of these issues yourself, but don’t hesitate to call a professional should you run into a problem you cannot handle.

Nonetheless, keep reading this troubleshooting guide for precise steps to fix a toilet tank that does not fill, but the water keeps running.

Kohler toilet tank not filling but water running

Toilet Tank Not Filling but Water Running (Problem & Fixes)

 ProblemPossible CauseFix
1.Leaking flapperOld flapper, debris, or flapper being too tight or looseReplace the flapper or the trip assembly.
2.Wrong height of the floatLow water level in the tankAdjust the water level in the tank.
3.Faulty fill valveDebris buildup or broken fill valveReplace the valve
4.Faulty overflow tubeDisconnection between the overflow tube and the fill tubeReplace the overflow tube
5.Water supply line problemsClogging or leakingCall a plumber
6.Low water pressure in the tankA partially closed fill valve or a rusty or leaking supply pipeSeek professional assistance
7.Issues with the trip assemblyMalfunctioning trip assemblyReplace the trip assembly
8.Toilet tank not filling at allDebris or worn-out fill valveReplace fill valve

1. A Leaking Flapper

The flapper lifts upward, allowing water from the tank to stream into the bowl, thus flushing it, then returns to its original position to reseal the tank and allow for water refilling. The flapper might be worn out and stuck open, or the stress in the chain may be forcing it to remain lifted if it fails to shut the drain hole during flushes.

In addition, don’t rule out a faulty trip assembly since the flapper connects to the flush lever and the flapper chain. Even though the water flows continually, if the flapper cannot achieve a good seal, the tank will not fill.

The handle being trapped downwards makes the flapper stay wide open, resulting in water trickling down to the toilet bowl from the fill valve. That’s why sometimes you may have to flush your toilet twice to clear a one-time mess.

Furthermore, chain may be too loose or tight is problematic for the flapper.


Examine the flapper chain linked to the flush lever arm by opening the tank cover. The chain should have a half-inch gap between the flapper at the tank’s bottom and the lever arm.

Ensure that the chain is neither overly tight nor attached to another section of the tank; otherwise, it can dislodge the flapper and cause the toilet to run continually. Also, ensure the chain is the right length to prevent it from getting caught in the flapper hole and closing correctly.

In addition, inspect the area near the flapper for debris. After fixing the problem, replace the cover and flush your toilet. If you’re still not pleased, examine the chain again, and fix it while slightly bending the rod.

2. Installing the Float at a Wrong Height

The float prevents the toilet tank from spilling after a flush. Typically, it rests on the water and controls water entering the tank after every flushing, pushing the float arm to close the valve, thus preventing water from entering the tank.

However, setting the float too low will inhibit its normal function by stopping the tank from filling completely.


  • Cut off the water supply to your toilet via the valve behind the toilet, or the primary home shutoff valve.
  • Inspect the float’s height and determine how much water you need to adjust.
  • Flush your toilet to discharge water and lower the height of the float.
  • Look for screws linked to the float while holding the lever arm down.
  • Use your screwdriver to turn the screws clockwise to boost the water level in the tank. Don’t apply excess force, as this might shatter the nut if it’s plastic.
  • Make sure the float is half an inch just below the overflow tube.
  • Allow water to enter by opening the supply valve.
  • Examine the height of the float.

NOTE: If adjusting the float is not your cup of tea, consider replacing it with a new one.

Toilet tank not filling quickly

3. Faulty Fill Valve

The fill valve inside the tank allows water from the supply to get into the tank after flushing. As a result, every time you flush, the bigger fill valve at the tank’s bottom releases water into the toilet bowl, while the smaller valve at the top opens for a water refill.

If a valve gets old or worn out, its performance will be below par. A blockage in the mechanism or occasional breakage could also contribute to fill valve woes.

It can create a scenario where the lower valve does not close, allowing water to constantly drain into the toilet bowl, while the higher valve does not allow enough water to enter the tank. You will observe water getting into the tank slowly or with low pressure.

Apart from that, the accumulation of debris can render your fill valve useless. It blocks water flowing into the toilet tank and creates low water pressure.


  • Stop the water supply to your toilet and flush out the water in the tank.
  • Release the fill valve by holding the shaft down and using a screwdriver to turn the fill valve cap anticlockwise.
  • Examine the area for debris or dirt buildup. If there is, wash it out and ensure it is clean before returning.
  • Insert the replacement fill valve and tighten the locknut. Continue twisting until you have a good seal.
  • Connect the overflow tube to the refill tube.
  • Allow water to enter the tank by opening the valve. Check the water pressure in the toilet tank.
  • Water should enter at the proper pressure and rise to the appropriate height.

4, Cracked Overflow Tube

The overflow tube may be unclipped from the fill tube since this can cut off water from the supply before refilling the tank. Apart from that, it might be worn out or damaged.


  • Get an overflow tube from a local store and replace the larger tubing in the middle of the toilet.
  • Yank out the faulty one and swap it with the one you bought.
  • Connect the refill tubing to the toilet tank to supply water to it.

5. Low Water Pressure in the Tank

Professionals suggest a fully functional toilet tank should take 10–20 seconds to refill. If it takes longer, you could be staring at a low water pressure problem, which will prevent the toilet tank from filling even with a non-stop supply of water.

Low water pressure could stem from a partially closed fill valve and a rusty or leaking supply pipe. If the fill valve is not wide enough, water will flow into the tank at low pressure, and the tank will take longer than usual to fill or not fill.


Contact a plumber to fix the problem.

How do you fix a toilet that won't fill the tank?

6. Issues with The Trip Assembly

The trip assembly connects the inside of the tank to the flush handle. If this component malfunctions, your toilet will not flush correctly, and the toilet tank will not fill as required after flushing.


Bend the broken trip back to its original place. Alternatively, use a paper clip to connect the flapper to the trip assembly temporarily.

However, the best solution is to replace the defective trip assembly with a new one.

7. Problems in The Water Supply Line

Leaking and clogging in the water supply line add to the list of what causes a toilet tank not to fill with water. The two problems occur from time to time, and if they go unattended could lead to significant damage to the floor, the drywall, and other structural elements.


  • Close the water supply valve on the wall.
  • Unplug the toilet supply line and direct it into a pail.
  • Restore the water supply and check whether you solved the problem.
  • If water keeps trickling, it shows the supply line is clogged. In this case, seek professional assistance.

8. Toilet Tank Not Filling at All

The toilet fill valve is the leading cause of a toilet tank not filling at all, stemming from debris buildup in the fill valve or having an old valve.


Replace the fill valve (Price on Amazon) as detailed above.

Final Remarks on Toilet Tank Not Filling but Water Running

Hopefully, this post has saved you from racking your brain for answers to why your toilet tank is not filling despite being connected to a water supply. Most of the problems highlighted here only need DIY diagnosis and resolution.

However, don’t hesitate to seek professional help in case of uncertainty.

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