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How to Fix a Slow Filling Toilet Tank

A slow filling toilet tank is one of the most common plumbing issues in many households. It’s not only frustrating, but it can also be very hard to diagnose especially if you have no idea how or where to start.

Typically, a normal functioning toilet tank takes an average of three minutes to refill. If your tank takes longer than this, then you definitely have an issue that requires your immediate attention.

Normally, when faced with this issue, most homeowners often seek the help of a plumber. Of course, this ends up costing them more money. The good news is that you don’t need to seek the services of a plumber to fix a slow filling toilet tank. You’ll need a little help to diagnose the problem though, and that’s exactly why I am here.

In this article, I am going to discuss all the possible reasons why your toilet tank might be filling slower than normal and I am going to recommend the best possible solutions for this annoying problem:


5 Main Reasons Why Your Toilet Tank is Filling Slowly and How to Fix It

The most common reasons why a toilet tank is not filling up as fast as it’s supposed to:

  1. Partially Open Water Supply Valve
  2. Faulty Water Supply Valve
  3. Debris Built Up in the Valve
  4. Clog in the Toilet Line/Tube
  5. Low Water Pressure
  6. Waterlogged Float Ball


1.     Partially Open Water Supply Valve

A partially open water supply valve is one of the most common causes of a slow filling toilet tank.

If you’ve recently noticed that the toilet tank is filling up slower than usual, it’s possible that the water supply valve (also known as the shut-off valve) is partially open.

The valve is located on the lower end of the water supply hose. It’s the knob protruding from the wall right below the toilet tank.

Someone may have interfered with it and this may significantly reduce the water flowing into the tank.

What you need to do is check if the valve is partially open.

If it is, be sure to open it completely for maximum water flow.

Another possible cause is build-up of debris which can restrict water flow, thus reducing the valve’s filling speed.

If there is debris inside the valve tube causing clogging, then you need to clean it up.

This actually brings us to our next possible cause of a slow filling toilet tank.


2.     Clogged Toilet Valve Tube

If opening up the shut-off valve solves the problem, then you’re good to go.

However, if this doesn’t work, you’re possibly looking at a clogged valve tube.

A lot of people don’t always realize that debris can actually clog the toilet valve tube and restrict water flow into the tank.

Usually, when debris builds up over time in the toilet water system which includes the shut-off valve, valve body, and supply line, the flow path of water becomes restricted. This slows down the speed at which the valve fills up the tank with water.

Lucky for you, this issue is usually an easy, hassle-free fix.

To unclog the toilet valve tube:

  1. Turn the shut-off valve and then unhook the line from the tank. Be sure to place a small bucket to catch any water still in the line
  2. Next, use a narrow bottle brush like the ALINK 5-Pack Bottle Brush Cleaner or a slim, long wire to loosen up the calcium and debris build-up causing the clog
  3. Once you’re sure that the clog has been removed, turn the water on to flush the debris out of the tube. To clear the tank off hard water deposits, rust, and calcium build up, I recommend adding a powerful toilet tank cleaner like the Instant Power 1806 Toilet Tank Cleaner. This toilet tank cleaner not only quickly remove calcium build up, rust, and hard water deposits- it also leaves a pleasant scent, not to mention prolonging the life of the toilet tank components
  4. Next, reattach the tube to the tank and turn on the water supply valve. Flush the toilet and check the water flow speed.
  5. If the water pressure increases, the problem is fully solved. If not, then it’s possible there is another underlying issue. There is a possibility that the water pressure is low or that the fill valve is faulty.

Let’s discuss the possibility of a faulty fill valve first.


3.     Faulty Fill Valve

If your toilet tank is filling slowly, the fill valve may be the culprit.

A fill valve’s job is to control the water levels in the toilet tank.

However, over time, the fill valve may become clogged with debris, calcium and other mineral deposits, shift out of alignment, or even stop functioning due to wear and tear.

Any one of these issues could be the reason why your toilet tank is taking too much time to fill up.

Let’s discuss how to fix each one of them:


Fixing a Slow Filling Toilet Tank Due to a Worn Out or Damaged Fill Valve

First things first, if the fill valve has been in use for more than 7 years, it may be too old and worn out. You’ll definitely need to replace it.

I am going to recommend one of the best fill valves in the market right now, the Fluidmaster 400CR Universal Toilet Fill Flapper Repair Kit for 2-Inch Flush Valves.

Fluidmaster 400CRP14 Fill Valve and...
  • FIXES NOISY, RUNNING TOILETS: Toilet repair kit replaces inefficient fill...
  • UNIVERSAL DESIGN: 400A toilet fill valve adjusts easily from 9 – 14...
  • CORROSION RESISTANT: Solid frame 501 2-inch flapper features...

This is a fill valve and flapper combo kit that is meant to replace a damaged fill valve and a leaky flapper. It’s the perfect solution for not only a slow filling toilet tank, but also helps fix a noisy and running toilet.

Since it’s universal, you can install it on any toilet tank model.

Installing both the fill valve and flapper is fairly easy. However, if you don’t want to go through the hassle of replacing it, you can hire a professional plumber to do it for you.


Fixing a Slow Filling Toilet Tank Due to Debris and Mineral Deposits

In some cases, the toilet may be filling slowly simply due to the presence of accumulated debris and mineral deposits in the fill valve.

A simple fix for this is to clean up all the dirt, flush the toilet, and see if it works.

To clean the toilet fill valve:

  1. Turn off the water supply and the flush the toilet tank
  2. Next, remove the top cap by reaching inside the toilet tank with your hand right under the float cup and gently lift it up. While doing so, ensure that the valve shaft does not turn and avoid the float cup from dropping
  3. Next, reach for the valve cap and turn both the cap and the lever counter clockwise at least 1/8 of a turn in order to unlock it. This will allow you to easily lift the valve cap and lever from the fill valve body
  4. After you remove the cap, check for debris and mineral deposits build-up on the valve part left in the tank and on the seal as well
  5. Next, hold the valve cap upside down over the opening of the fill valve and then turn on the water supply full pressure for a few seconds. The high water pressure will loosen up any debris or mineral deposits inside the valve
  6. Finally, reassemble the valve cap and flush the toilet. If removing debris doesn’t work, the only option you have is to either repair it or replace  the entire valve


Fixing a Slow Filling Toilet Tank Due to Fill Valve Misalignment Issues

Sometimes, the fill valve shifting out of alignment can prevent the toilet tank from refilling properly. Luckily, this is one very simple fix.

To adjust a misaligned fill valve:

  1. Remove the toilet tank lid and locate the fill valve. You’ll find it at the left side of the tank
  2. If yours is the newer toilet model, turn the adjustment knob of the fill valve with your hand. This will allow more water to flow into the tank. If yours is an older model, you’ll need to use a flathead screwdriver to loosen up the adjustment screw. Next, raise the fill valve to let more water into the tank
  3. Next, ensure that the tank’s water level is at least 1-inch below the top of the overflow tube
  4. Lastly, flush the toilet and check to see if the tank fills up as fast as its supposed to with the right amount of water

These three solutions should help solve the slow filling toilet tank issue. Remember, if the fill valve is damaged, getting a replacement is highly advisable.


4.     Low Water Pressure

The most common causes of a slow filling toilet tank include partially open water supply valve, a clogged water valve tube, and a faulty fill valve.

However, in some cases, there might not be any issue with the toilet tank at all. The problem can arise as a result of a sudden reduction in water pressure.

The issue is actually easy to diagnose as you’ll also notice less amount of water coming out of the bathroom and sink taps.

In most cases, low toilet water pressure is often as a result of a leakage or blockage in your toilet plumbing system.

No matter how high the water pressure is in the pipes, if it encounters a damaged pipe or a blockage, the pressure will greatly reduce. This of course causes the tank to fill up slower than usual.

Fixing low water pressure is not something you can handle on your own without the right tools or knowledge. Plus this is clearly an issue that extends beyond your bathroom.

I recommend seeking the services of your local plumber to solve the low water pressure problem.


5.     Waterlogged Float Ball

Another rampant cause of a slow filling toilet is a waterlogged float ball.

A float ball typically floats on top of water in the tank reservoir.

Its main purpose is to control the amount of incoming water. It does so by using an arm that is attached to it to stop more water from entering the tank.

If the float ball happens to be waterlogged, it will prevent the toilet tank from filling efficiently. As a result, it may cause the tank to refill at a much slower rate or even prevent an adequate amount of water to enter the tank.

The good news is that fixing a waterlogged float ball is easy and quick.

The first thing you need to do is check the water level of the tank.

If the float ball is not floating near the top of the tank or if the tank is partially full, chances are that the float ball is waterlogged.

One possible reason for this is if the float ball has been fixed too low. This reduces the amount of water entering the tank.

To fix this, slightly bend the  float arm upward. This will raise the float ball and thus allow more water into the tank. Of course, this will increase the refilling speed.

If this simple fix doesn’t solve the issue, then you might want to consider replacing the float ball.

The Kerick Valve PF06 Polyethylene Sphere Float Ball is one of the best float balls in the market.

Kerick Valve PF06 Polyethylene Sphere...
  • For use with 3/8" to 1" inlet float valves and 1/4"-20 threaded rods (sold...
  • Polyethylene for chemical resistance
  • 1/4"-20 female threads for mounting

The float ball is designed for use with 3/8-inch to 1-inch inlet float valves and ¼-inch to 20 threaded rods.

Installation is easy and hassle-free. All you have to do is pull the old one off the float arm and replace it with the new one.


How to Fix a Slow Filling Toilet Tank: The Bottom Line

A slow filling toilet tank can be frustrating, especially if yours is a large family.

With such a tank, family members have to wait a long time for the tank to refill before using the toilet. You know how annoying this can be.

Fixing a slow filling toilet tank is not always complicated especially if you how to properly diagnose the problem.

Of course, you can always seek professional plumbing services but it would save you a lot of money if you simply do it yourself.

Hopefully, this guide will help you quickly diagnose and fix your slow filling toilet tank.

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