Why Is Your Toilet Tank Not Filling But Water Running? (Fixed!)

Imagine knowing the water is running, but your toilet tank cannot fill. This issue is sure to frustrate you as it makes flushing your toilet impossible, so it makes sense to want to get to the bottom of the toilet tank not filling but water running.

Water runs, but your toilet tank is not filling because of a faulty fill valve, water supply problems, an obstructed fill tube, float issues, or a misaligned flapper. The culprit could also be water pressure issues, a leaking tank, or debris in the valve.

To fix this problem, you must get to the bottom of it, exploring the causes and then fixing them. This post addresses this issue in detail.

why is my water tank not filling up

Toilet Tank Not Filling But Water Running (Causes & Fixes!)

 ProblemPossible CausesRecommended Fixes
1.Faulty Fill ValveDebris or sediment buildup
Worn or damaged fill valve
Clean or replace the fill valve
2.Water Supply IssuesPartially clogged supply line
Frozen or blocked pipes
Sediment buildup
Supply line leaks, cracks, or damage
Open the water supply valve Thaw the pipes
Clean or flush the valve and pipes
Replace damaged or leaking water supply line parts
3.Obstructed Fill TubeKinked or blocked fill tube
Debris or mineral buildup  
Straighten the fill tube gently Clean the fill tube
4.Float IssuesStuck float
The float set at an incorrect level Mineral or debris deposit
Ensure the float isn’t obstructed
Adjust the float height
Clean the float
Address leaks
5.Misaligned FlapperLong chain
Misaligned or damaged flapper Debris accumulation  
Adjust the chain length
Ensure the flapper and its seat are well-aligned
Remove debris
Replace the flapper
6.Water Pressure IssuesMineral deposits or debris buildup inside the pipes
Plumbing system leaks
Old or corroded pipes Malfunctioning water pressure regulator or pressure-regulator valve
Clean the pipes
Locate and repair leaks
Repair or replace old pipes
Adjust or replace the water pressure regulator or pressure regulator valve
7.Leaking TankWorn-out or loose bolts and washers
Damaged gaskets and bolts
Cracks, holes, or damage inside the tank
Damaged tank
Tighten loose parts
Replace damaged components

1. Faulty Fill Valve

Typically, the fill valve refills the tank following a flush. However, if it malfunctions, it might cause water to run continuously without filling the tank.

Check whether the fill valve is stuck in a closed position or only partially open, as that will restrict the flow of water into the tank. This can lead to a situation where the toilet keeps running, but not enough water enters the tank.

Also, check for debris or sediment that might be blocking the fill valve, preventing it from opening or closing correctly. This can disrupt the water flow and cause the tank not to fill properly.

Moreover, the fill valve and its components could be worn out, affecting its functionality.


After stopping the water supply and flushing your toilet, look for the fill valve, usually a vertical assembly connected to the water supply line. Use a soft brush, cloth, or small tool to clean away any debris or dirt buildup.

Remove the fill valve filter, if present, and then clean it of any sediment or debris blocking water flow.

Replace the fill valve if it is damaged or worn out.

2. Water Supply Issues

Water supply-related issues like a partially clogged supply line, frozen or blocked pipes, sediment buildup, or supply line leaks, cracks, or damage can cause issues filling the toilet tank. While your toilet tank will fill, it will just take longer.

A partially closed water supply valve can restrict water flow to the toilet tank. The same happens if the water supply line is partially clogged.

Moreover, in cold weather, pipes can freeze, causing water flow reduction or blockage. Therefore, check for signs of frozen pipes, such as frost on exposed pipes.

In addition, inspect the water supply line for leaks, cracks, or damage because even a tiny leak can significantly impact water flow. Also, over time, sediment and minerals can accumulate in the water supply valve and pipes, affecting water flow.


  • Rotate the valve counterclockwise to open it.
  • Clean or replace the supply line.
  • If you suspect frozen pipes, thaw them carefully to restore water flow. However, if unsure, contact a plumber.
  • Replace any damaged or leaking parts of the water supply line.
  • You should also clean or flush the valve to improve water flow.
Toilet tank not filling with water at all

3. Obstructed Fill Tube

The fill tube, a small plastic tube, directs water into the overflow tube in the toilet tank. For this component to function properly, it should be connected correctly and not obstructed.

However, the fill tube can sometimes become twisted or blocked, preventing water from flowing correctly.


  • Stop the water supply before working on your toilet, take out the lid, and find the fill tube.
  • Check the fill tube for any kinks, bends, or obstructions.
  • If the fill tube is kinked or bent, gently straighten it out to ensure water can flow freely through it.
  • If you suspect debris or mineral buildup inside the fill tube, use a flexible brush or a thin wire to remove any obstructions carefully. Be gentle to avoid damaging the tube.
  • Make sure the fill tube is securely attached to both the fill valve and the overflow tube or bowl, depending on your toilet’s design.
  • Turn the water back on, then observe whether water is now flowing into the tank without any issues.
  • Flush the toilet to see if the water level in the tank drops as it should, and then refills properly through the fill tube.
  • Keep an eye on the toilet over the subsequent few flushes to ensure that the tank is filling as it should and that there are no signs of leaks or overflowing.

4. Float Issues

The float regulates the water level in the tank, but this is only possible if this mechanism works properly. If your toilet float gets stuck in the “up” position, it might prevent the fill valve from opening fully.

Additionally, debris or mineral deposits can collect on the float, causing it to become heavy and malfunction. Ballock-style fill valves are less common in modern toilets, but check for leaks around the valve if yours has one.


  • Stop the water supply, open the toilet lid, flush the toilet, and watch the float as the tank fills. If the float doesn’t rise as the water level increases, it might be stuck or not moving freely. Make sure any parts inside the tank do not obstruct the float.
  • Bend the float arm or adjust the screw or clip to adjust the float. The goal is to set the float to the correct level that triggers the fill valve to shut off when the water reaches the desired height.
  • Clean the float to ensure it’s buoyant and can move freely.
  • Address any leaks around the float.

5. Misaligned Flapper

Your toilet flapper might be malfunctioning if the water runs continuously without filling the tank. Typically, the flapper should open when you flush and then close tightly when the tank is refilling, so if it’s not closing correctly, it might be misaligned or damaged.

The flapper might not close well if the chain is too long. You should also examine the flapper for objects or debris preventing the flapper from closing fully.

Furthermore, check the flapper for deterioration, damage, or cracks because these issues can make the flapper not close correctly. In addition, make sure the flapper is appropriately aligned with its seat because the flapper can sometimes become misaligned, preventing a proper seal.


  • Adjust the chain length so there is a slight amount of slack to let the flapper close wholly.
  • Clean the area around the flapper to remove debris and sediments.
  • Adjust the flapper so that it fits snugly and seals the drain opening when closed.
  • Replace the flapper with a new one. Korky 100BP Ultra High-Performance Flapper (View on Amazon) is an excellent choice since it is durable, easy to install, and fits most toilets.
Toilet tank not filling with water after flush

6. Low Water Pressure

Low water pressure can affect the proper functioning of the fill valve. Therefore, check other fixtures in your home to see if the issue affects the entire plumbing system.

Turn on faucets and other fixtures in various parts of your house to see if the water pressure is consistently low. The problem may be related to the main water supply if multiple fixtures are affected.

Remember that pipe obstructions, pipe leaks, or using old or corroded pipes can cause low water pressure.

While troubleshooting low water pressure, check the pressure regulator to determine whether it’s malfunctioning. Also, check your pressure-reducing valve (PRV) if your home has one to see if it’s faulty or set low.


  • Assess and clean the pipes to eliminate mineral deposits or debris buildup.
  • Inspect your plumbing pipes for corrosion or damage, then replace or repair the affected parts.
  • Adjust or replace the water pressure regulator or PRV.

7. A Leaking Tank

As you inspect the inner parts of your toilet tank, like the flapper seal and flush valve, for leaks, do not overlook the exterior. This is because a crack in the tank can make the water drain faster than it’s being refilled, leading to continuous water flow without filling the tank.

Examine the bolts and washers since they can become loose or deteriorate, leading to leaks. Also, inspect the gaskets and seals inside the tank.

Leak detection tablets can help you identify the source of a leak. Drop a tablet into the tank and wait a few minutes. A change in the water color inside the bowl indicates a leak from the tank into the bowl.


  • Tighten any loose bolts and replace any damaged washers.
  • Replace worn, cracked, or malfunctioning gaskets and seals.
  • Replace the tank if it has extensive cracks or irreparable damage.

Summary of Toilet Tank Not Filling But Water Running

As you can see, water running without filling the toilet can be attributed to several factors. Therefore, by understanding the basics of toilet mechanics and following the diagnostic steps outlined above, you can identify the root cause of the problem and take appropriate actions to resolve it.

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