Why Does My Toilet Fill Slowly? How To Fix It?

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Last Updated on December 30, 2022 by acechapman

If you have a toilet that starts to fill slowly, it can be frustrating and inconvenient. A slow-filling toilet may take longer to refill after each flush, and it can also waste water if the problem is not addressed. In this article, we will discuss some of the common causes of slow-filling toilets and provide steps for how to fix them. By understanding the underlying cause of the problem and taking steps to repair it, you can help ensure that your toilet functions properly and efficiently.

Problems with the flush valve or recharge valve are the main reasons why your toilet tank isn’t filling up. Your toilet may take too long to fill due to a few factors, such as a floating valve or water pressure.

What causes a toilet to fill slowly after flushing?

Your toilet tank may not be filling properly for several reasons. The main reason your toilet tank is not filling properly could be the issue with the flush flap, or the refill flap. Water pressure and shutting off the water are other possible causes.

Before we get into the causes, we’ll tell you about the toilet flush mechanism.

The main three components of a toilet tank are the flush button and lever, which do not cause filling up.

Fill Valve

The water supply tank’s fill valve, also known as the refill valve, is connected to it by the fill valve. This valve is responsible for refilling the tank following a flush.

The fill valve connects to the refill tube as well as the toilet float. The shape of the toilet float can vary between older models and newer ones.

Fill valve mechanism:

  • After flushing, the water released for cleaning purposes next to the floating moves to the bottom of the toilet tank.
  • Then, the water fills the tank.
  • The float will continue to move up until the tank is filled.
  • This refill tube sends water to the bowl via an overflow tube, which prevents gases.

Flush Valve/Flapper

The flapper is a rubber sealing container that is placed into the hole or drainage line leading into the bowl.

Through a chain, the flush valve is connected to the flush handle. You should leave 1/2 inch of slack on the chain.


  • After each flush, the lift chain opens the flapper. The water will then flow into the bowl through the siphon jets.

Overflow Tube

It is a large tube that runs through the middle of the tank. This is the main channel where excess water runs and prevents overflowing. You may have to fill the toilet tank if the overflow tube is damaged.

For a diagnosis, examine each one carefully.

why does my toilet fill slowly

Factors why the toilet tank is not filling up

Toilet Tank Fill Slowly After Flushing

  • If the tank is empty, check the refill valve. The problem could be a defective refill valve. The toilet tank will not fill.
  • If there is any debris in the fill valve, the water won’t come to the tank enough or it will cause the toilet tank to fill slowly.
  • Also, inspect the water supply tank. There may be plaques or debris on older water supply tanks. The slow-filling toilet could be a problem due to insufficient water supply.

Toilet Tank Not Filling Up Enough Water

You can read the part about the toilet and you will see that I said the floating ball is responsible to maintain the water level.

The floating ball should be checked. If it is too low, the tank may not be filling up enough.

Toilet Tank Not Filling, But The Water Is Running

Three reasons that might cause this problem.

Flush valve

A defective flush valve is one of the most common causes. If the flapper or flush valve is damaged, the tank’s water will leak and start to overflow.

This means that all of the water is drained out at once, even though the water has been filling up.


If the flush valve is not faulty, check the refill valve that is connected to the float. The bowl will burst if the float level is too high.

Adjust the float level, and then wait for a while to see what happens. The same scenario is repeated, but this time look for the overflow tube.

Overflow tube

While overflow tubes can sometimes crack, they continue to send water into the bowl and don’t fill the tank.

Other Two Reasons For Slow-Filling Tank

After having seen so many things, if none are defective, there are two other options.

Shut Off Valve

Make sure you open the shut-off valve correctly. The shut-off valve might not open the water supply to the tank.

Water pressure

This will be your last verifying point. Check your water pressure if your fill valve and flush valve are in good shape.

Low water pressure is the main reason you don’t have enough water.

You won’t be able to do this again. Talk to your water supplier.

Hacks for other problems can be found that are quick and easy to solve in less than 5 minutes.

You now know why the toilet tank is taking too long to fill after flushing. You can find out how to fix slow-filling toilet tanks.

why does my toilet fill slowly

How to Fix A Toilet Tank That Fills Slowly?

Replace The Fill Valve

The toilet refill valve regulates the water level in the tank. Replace it or check every five years.


  • Before you replace the tank, make sure to check for any debris. Turn off the water supply line to the tank.
  • To flush the toilet completely, make sure that no water remains in it.
  • To lift the cap, place one hand on the bottom of the refill tube. Then, rotate the cap clockwise.
  • Be sure to check the tube for any debris.
  • You can avoid water splash by securing the refill cup and opening the water supply to allow water pressure to remove any debris.
  • You can inspect the contents and then place the cup into the fill tube.
  • Inspect it thoroughly.
  • Wait for 10 minutes. The efficient tank’s water level is normally full. If it doesn’t, replace the refill valve.

How to Replace a Refill Valve for Slow-Filling Toilet Tanks?

  • Switch off the water supply to the bathroom at first.
  • For water drainage, flush the tank thoroughly and then remove the tank cover.
  • Disconnect the water supply.
  • Change the fill valve from the original to the new. Follow their instructions.
  • You can also match the size refills and purchase them exactly.
  • Before placing, clean the refill valve from the surrounding area.
  • Attach everything to the valve as you did before.
  • Connect the refill tube to your overflow tube
  • Connect the water supply line to the mains and then open it.
  • Next, check the filling amount.
  • This entire process takes 45 minutes to 1 hour or less.

Fixing a Toilet Tank That Doesn’t Fill Up With Enough Water

  • This can be caused by changing the floating ball from an old to a new toilet.
  • You can adjust the height of the floating ball by simply increasing its size.
  • There are many styles of floats.
  • The float hangs from a rod attached to a wire at the end of the bathroom’s older bathrooms. The water valve is usually equipped with bolts.
  • The screw would adjust the level at which the water valve shuts off.
  • If the metal is not tightening, or the limit has reached its maximum, you can bend on it.
  • You will find the float around the neck of the filling valve in new toilets. It goes up. The spring strap is attached to the float by a rod made of metal that connects with the valve shut-off. To move the float, you can squeeze the spring clip upwards or downwards on the rod. You can now use the spring clip to fill the level.

How to Fix a Toilet Tank That Is Not Filling but Water Running

Replace The Flush Valve

  • Replace the defective flush valve with a new one.
  • The shutoff valve is located just behind the toilet bowl.
  • Make sure to flush the toilet thoroughly and drain any excess water.
  • Remove the toilet cover/lid and then remove the lift chain from its flapper.
  • Next, remove the flapper hands that attach to the overflow tube.
  • Clean the area after you have unhooked the flapper and then place the new one.
  • Attach the overflow tube to the hook on the lift chain
  • Connect the water supply to the toilet tank and monitor for running water.
  • Cover the lid.

How to Replace the Overflow Tube

  • It is very simple to replace the overflow tube.
  • Drag the old valve out and place it there.
  • Keep in mind that the new overflow tube should be the correct size.

How to Fix The Water Pressure

I will now show you how to check your water pressure. Check all fixtures for water pressure. If the water pressure is only an issue, then low water supply affects all fixtures.

For help, call a professional plumber.


To sum up, if you have a toilet that fills slowly, it could be caused by a variety of issues, including a clogged vent stack, a clogged toilet, a faulty fill valve, or a faulty flapper valve. To fix the issue, you may need to try using a plunger to remove any blockages, or you may need to identify and repair the faulty component.

If you are not comfortable doing this yourself, it is recommended to call a plumber for assistance. By addressing the issue, you can help ensure that your toilet functions properly and efficiently, conserving water and saving money on your water bill.

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