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Toilet Tank Not Filling With Water: Why & How to Fix It

A well-running toilet is probably one of the least appreciated parts of a home. But when it’s not working properly, then the entire household is disrupted. The horror of suddenly not being able to flush the toilet because the tank is not filling with enough water is overwhelming.

Thankfully, the toilet design is pretty straightforward. Problems happen, but they are typically easy and quick to troubleshoot – no need to frantically call for a plumber.

So, if you’re wondering why the toilet tank is not filling with water or filling slowly, here are the most common reasons for it, plus a few fixes to get your toilet running again in no time.

half empty toilet tank

7 Reasons Why Your Toilet Tank Is Not Filling Up and What to Do to Fix It

1. Closed Shut Off Valve

Your toilet tank is designed so that it’s refilled with water every time you flush the toilet. But if the tank is not filling up, or no water is filling the tank at all, the first thing you will need to check is whether the shut-off valve is open or not.

Perhaps, someone was tinkering with the water supply pipe to the water tank and forgot to turn the valve open afterward.

How to Fix It

Turning the shut-off valve to its “open” position is a super easy fix: just turn the valve counterclockwise. This should open the valve up and send water right into the tank.

If, however, the shut-off valve is in the “open” position, but still, no water is filling the tank, then the problem could be a stuck valve or a partially closing valve.  In this case, you may have to replace your toilet’s shut-off valve with a new one that works more smoothly.

2. The Toilet Float Ball is Set Too Low

Another reason your toilet tank may not be filling with water is that the toilet float is set too low. This float cup or float ball, in older toilet models, is connected to the tank’s fill valve, controlling its opening and closing.

When the toilet float is set too low, the opening for the water to fill the tank will be too small. Hence, the toilet tank will still fill with water, but the level of water will be very low.

How to Fix It

You will need a screwdriver to readjust the toilet float. Start by first turning the shut-off valve closed, then flush the toilet to take out most of the water inside the tank. Remove the lid and check whether your toilet tank has a float cup or a flat ball.

Older models with a float ball are usually connected to an arm, which is then connected to the toilet’s fill valve with a screw. Use a screwdriver to adjust the float so that the level of water should be around ½-inch below the overflow tube.

If your toilet has a float cup, adjust the plastic screw connected to the float.

3. Faulty Fill Valve

Your toilet’s fill valve is the one responsible for supplying water inside the tank after flushing. It’s connected to the bathroom’s water supply line, refill tube, and the toilet float on the inside of the tank.

Even with the toilet float working properly, the tank may still not fill with water because of a faulty fill valve. Usually, the reason for this is the accumulation of dirt and debris in the valve.

How to Fix It

Remove the fill valve and inspect the holes inside the valve for any debris and dirt that could be blocking the water supply. Remove any possible clogs and put the fill valve back on the toilet tank.

If you notice that the fill valve is already worn out, especially the seals, it might make more sense to replace it with a new one than to repair it.

4. Loose or Worn-Out Toilet Flapper

Another probable reason why your toilet tank is not filling up with water after flushing is because of a loose or worn-out toilet flapper. The toilet flapper is a rubber seal that sits at the bottom of the tank; it opens and closes to allow water to enter the toilet bowl.

If the toilet flapper doesn’t seal completely, water will leak into the toilet bowl. Hence, the tank won’t hold water for the next flush.

How to Fix It

Sometimes, debris and mineral buildup prevent the toilet flapper from sealing shut. Cleaning it will likely resolve the issue.

But if the flapper has noticeable warps and worn-out surfaces, it will need to be replaced to avoid a running toilet that keeps the tank from filling with water.

5. Cracked or Broken Overflow Tube

Your toilet’s overflow tube is that large tube you can find in the middle of the tank. It channels excess water down into the toilet bowl, preventing overflowing in the toilet tank.

The problem with overflow tubes is that they are often made of plastic, prone to cracking over time. Once there’s a crack in the tube, water from the tank will leak into the toilet bowl. It’s the same problem you have with a loose toilet flapper – a running toilet and a tank that never fills with enough water.

How to Fix It

There’s only one thing you can do if the problem is a broken overflow tube – buy a new one. Because once the overflow tube breaks and starts leaking, there’s no repairing it. But remember to get the right size flow tube for your toilet.

6. The Water Pressure to the Toilet Tank Is Too Low

Your toilet tank might still be filling with water, but what if it’s too slow? The problem could be that the toilet water pressure is too low, and there are a couple of reasons this might be the case. You could have leaky water pipes somewhere or just a clogged section of a pipe.

How to Fix It

The first thing you need to do if you have this issue is to trace your toilet’s plumbing system. Is the low water pressure only a problem in the toilet, or does it also affect other fixtures in your home?

If the problem is only in your toilet, start by checking for clogs in the toilet’s supply line. But if the issue affects the entire house, you might need to get a professional to address the problem.

7. Broken Toilet Bowl

Lastly, if the toilet tank is still not filling with water despite all the fixes above, it could be that the toilet tank is not the issue. Perhaps, you have a broken toilet bowl. Although this problem is less common than the ones articulated above, toilet bowls can crack and cause water leaks to the bathroom floor.

If you notice that the toilet tank is always empty and there’s an obvious puddle on the floor, you could have a broken toilet bowl.

How to Fix It

The only fix for this issue is to take out the old and broken toilet bowl and replace it with a new one.

Kyle Tucker

Kyle from Kyle Tucker Plumbing is a certified plumber with over 20 years of professional experience installing plumbing fixtures such as bathtubs, sinks, and toilets, as well as installing gas lines and water pipes, performing bathroom repairs, and more.

Kyle knows how to deal with every plumbing issue that modern homeowners encounter, and he shares his lifelong experience with readers in an engaging and easy-to-digest way.

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