5 Reasons Why Your Toilet Tank is Not Filling With Water and How to Fix It

When a toilet tank is not filling with water when it needs to, it can be an absolute pain in the butt. But what are the most common reasons why this might happen? Well here are the 5 main reasons, along with solutions that will help!

If your toilet tank is not filling with water, it could be for one of five reasons. These include: 1.) the float ball height needs adjusting 2.) the fill valve needs replacing 3.) the flapper is not sealing correctly 4.) there’s a leaky or cracked overflow tube, or 5.) the water supply line could be blocked. If you want to know what might be causing this issue with your toilet, read on!

5 Reasons and Solutions for a Toilet Tank That Won’t Fill Properly

1.) Toilet tank not filling with water because float ball/float arm is the wrong height:

The first thing you might want to check is the height of your toilet’s float arm. Float arms control the float ball and how much water fills your tank after each flush. You can determine if it’s at the right level by carefully bending it up or down until the water and float ball rises to where it should be. If you can’t adjust it, then it’s likely that the arm has broken and needs to be replaced.

Newer toilets will have a cylinder float. To adjust one of these, you simply raise or lower it using the adjustment clip.

2.) Toilet tank not filling at all or too slowly because the fill valve needs replacing

Fluidmaster Fill Valve: Image from Fluidmaster.com

If your toilet tank isn’t filling with water at all or very slowly, it could mean you have a faulty fill valve. This is usually due to the bottom washer deteriorating or the fill valve just not working properly anymore. Fill valves need replacing if it is leaking or the water level in the tank isn’t rising.

Here are step by step instructions on how to replace toilet fill valves :

Step 1: Check for leaks

Take a close look underneath the tank where the fill valve is connected to the water pipe. See if there are any leak problems. If you can see water leaking down the water supply line then you will need to replace the damaged washer.

Step 2: Check to see if the toilet fill valve is flowing correctly

Over time, fill valves accumulate minerals that will build up inside, causing it to leak or have blockages. Take off the toilet tank lid and place a bucket under it. Turn off the water supply using your shutoff valves.

Flush the toilet to drain any excess water in the tank so you can see inside when you remove the top part of your fill valve. Once removed, take a look inside and if you see mineral build up in there, all you have to do is remove any gunk with an old toothbrush.

Step 3. Replace old fill valve but keep base

It is recommended that fill valves are replaced every 5 years. If you feel that your fill valve is due to be replaced then it is quite easy to do the job yourself.

Remove the toilet lid, turn off the water supply and then flush the toilet to empty the tank.

If the base of the fill valve is in good condition then the upper area of the valve is all that is needed to replace.

After the old fill valve is removed from its base, the new fill valve can slide onto the base and then locked into place.

Step 4: Replace complete toilet fill valve

With the water turned off and toilet already flushed, place a plastic container under the tank and unscrew the hose.

With a rib joint pliers remove the nut and then carefully remove the fill valve as it will still have water inside it.

Place new fill valve into the hole and thread the lock nut by hand and then tighten with the pliers.

Reattach the hose and then attach the fill valve’s fill tube to the overflow tube.

Check if it is working by turning back on the water and flushing the toilet again. If all is well and water is flowing from the fill tube into the overflow tube, then your problem should be solved!

3.) Toilet tank won’t fill because the flapper is not sealing correctly

toilet flapper
Korky Toilet Flapper: Image from Korky.com

Toilet not filling because the flapper is not sealing correctly? Try re-seating it to ensure that it has a good seal. If that does not fix the issue, then you may have to replace your worn out flapper.

To replace a flapper follow these steps:

Step 1. Turn off the water supply

Turn off the shut-off valve and then flush the toilet. Hold the handle down to make sure the tank is fully emptied.

Step 2. Unhook the flapper chain

Unhook the flapper chain from the flush lever and then unhook/unclip the flapper from the flush valve.

Step 3. Clean valve seat

Give the valve seat a clean if it is dirty. (Use a wet cloth/paper towel)

Step 4. Attach new flapper

Attach your new flapper by hooking the flapper ears to the hooks on the flush valve.

Step 5. Attach flapper chain

Attach the flapper chain to the flush lever. Allow minimal slack and trim any excess chain.

Step 6. Turn water supply back on

Turn the water valve back on and refill the tank.

4.) Toilet tank not filling with water after flush because there’s a leaky or broken part of your overflow tube

The toilet overflow tube is an essential part of your tank because it stops your tank from overflowing by channeling any excess water down into the toilet bowl.

If there is a crack or leak in the overflow tube, the tank will not be able to fill up with water.

To replace the overflow tube, it is probably a good idea to replace the entire flush valve. This requires removing the tank first, which sounds complicated but is not as difficult as it sounds.

Here is a detailed video to show you how to replace a flush valve:

5.) Water tank is not filling because water supply not fully on

If you’re certain the shut-off valve is fully open, but the toilet tank still won’t fill up after flushing, make sure there’s enough pressure so that the water fills properly. When water pressure is low, your tank will fill up very slowly. This may be caused by clogged or leaking pipes.

First of all, make sure that the low water pressure is only in your toilet and not in other rooms as well. If it is only in your toilet, then you can check if the supply line is blocked.

To check to see if you need to replace your water supply line, turn off the water. Flush the toilet. Unscrew the water supply from the tank and empty any excess water flow into a basin. Then turn on the the water supply to see if water is going to flow into the basin. If it doesn’t, then the water supply line may need to be replaced.

Conclusion to your toilet tank not filling with water

When toilet tanks do not fill with water, there are five potential reasons why.

These include the float ball and float arm not being the correct height, a faulty fill valve, parts of your overflow tube leaking or broken, or maybe a blocked water supply line.

In any case, if left unchecked for too long it could lead to serious damage and costly repairs down the road.

Make sure you know what’s causing this issue so you can get started on fixing it right away! If you’re not sure which of these reasons is the culprit, call a professional plumber to come and diagnose the problem.

They’ll be able to help you determine if it’s something minor that can be easily fixed or an expensive repair job waiting for your approval.

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