Why Does My Toilet Flush Twice?

If your toilet has been flushing twice recently, you may be wondering what is going on. Don’t worry, you’re not alone! This is a common problem that many people experience.

What do you think, why does your toilet flush twice? There are two primary causes of double flushes in the toilet. Firstly, a faulty flapper valve that stays open for too long or doesn’t seal the valve properly.  Secondly, an improperly set refill valve floods the tank and forces it to flush again.

Further in this article, we will discuss these causes in detail, and how you can fix the issue in each case. But to understand why double flush occurs, you need to understand the role of the flapper valve and refill tube in the functioning of a simple toilet.

Let’s understand that first. 

How does a Simple Toilet Function?

The commonly used toilets in our bathrooms are gravity-flush toilets; their history is as old as 200 years. A gravity-flush toilet primarily has two parts: a bowl and a tank. The tank holds the clean water from the main supply line. When you flush the tank, this water goes into the bowl due to gravity and stays there until the next flush. In addition, there is an opening in the middle of the bowl that links the toilet to the home’s plumbing system through a siphon.

Parts of a Toilet Tank
Parts of a Toilet Tank

Now, the main thing to understand is the mechanism of flushing; how does the water move down to the bowl when the lever is pushed? The flush button is attached to a lever on the tank’s inside. The lever is further connected to the flapper valve via a small chain, which lifts the valve up and down on the action of the flush button.

When you flush, the lever lifts the flapper valve, and the whole water moves down to the bowl and pushes down the old water into the drainage pipes, due to the vacuum created by the siphon.

Thereafter, freshwater is supplied through the toilet’s supply valve to the tank fill valve, which is located inside the tank. Once the tank empties between flushes, this is how it re-fills and prepares itself for the next one.

Causes of Double Flushing in the Toilet

If the flapper, refill valve, float, or any portion of the toilet malfunctions or ceases operating, the toilet may flush twice. But mainly, the two main culprits of double flushing are bad flapper and refill valve.

Let’s discuss how can you fix each of these.

A rubber flapper valve stays open

Cause # 1: Bad Flapper Valve

If the flapper stays open for too long, then it lets the water go into the bowl.  One of the reasons why this happens is a lightweight flapper valve.

Had you replaced your toilet flapper in the past?  If yes, then you might have replaced it with a universal flapper rather than its actual flapper. The universal flapper is slightly lesser in weight compared to the actual flapper designed for the toilets. So, it fails to fall into its position timely to seal the tank. That is why, after one flush you observe another flush.

Even if the tank holds the right kind of flapper, at times it may need a replacement. For instance, if your toilet was not used for an extended length of time, and if there was no water in the tank. The flapper may have become excessively dry, causing the rubber to become less elastic or even prone to breaking.

In some cases, if the flapper is adjustable. Then, its maladjustment might have caused the double flushing.

Now, to diagnose the cause you can test your toilet by removing the tank cover and flushing it. Watch whether the chain connecting the toilet lever to the flapper is short, obstructing it to close. Is the flapper too dry and not falling on the valve?  

Based on what you observe, decide whether it needs an adjustment or complete replacement.

How to fix the adjustable flapper valve?

If you have an adjustable flapper which has a dial on it, first you should try to adjust it. There are chances your problem might get resolved.

To correctly fix the adjustable flapper, follow the step-wise procedure mentioned below:

turning shut-off valve
  1. Cut off the water supply. This can be done by turning shut-off valve (at the back wall adjacent to the toilet) clockwise.
  2. Flush multiple times to make the tank empty.
  3. Take off the tank’s covering and place it somewhere safe.
  4. You may notice some remaining water in the tank. Using a cloth, remove that water. Once the water is removed, you can easily put your hands on the flapper.
  5. Turn the flapper’s dial to open bigger holes. The bigger perforations will allow the air held in the flapper to escape faster. As a result, the flapper will return to its proper position as quickly as it should.
  6. Place the tank’s cap back and turn on shut-off valve.
  7. When the toilet tank gets filled with water. Flush it and see if flushes properly.

How to replace a Flapper Valve

If your toilet doesn’t have an adjustable flapper, instead its flapper is dry and cracked. Then you might need to replace it. For doing this task properly, you can follow the mentioned steps:

  1. Turn off the water supply to the toilet by turning the shut-off valve clockwise.
  2. Flush the toilet to drain most of the water.
  3. Take off the tank’s lid.
  4. Since the flapper is attached at the base of the tank, you need to remove the remaining water to get your hands on it.
  5. Take a towel or sponge to remove the water.
  6. Unclip the old flapper, the chain also comes off. Also, disconnect it from the overflow valve.
  7. Place the new flapper valve in its place, and link to the components from which you removed the past flapper. Keep in mind to adjust the length of the chain.
  8.  Close the tank by placing its lid back.
  9. Turn on the water. Once the tank refills, flush it and see if the problem is resolved.
toilet tank with refill valve
Image from Your Santa Clarita Handyman

Cause # 2: Incorrectly set Refill Valve

A faulty refill causes the tank to get overfilled. If the tank is overflooded with water. Then, when you flush it once, the extra water being in the tank rushes to the bowl creating a second flush.

In this case, one thing that you would notice is a powerful flush followed by a weak flush.

To diagnose this issue, you need to take off the tank’s lid and see the water level. If it’s filled beyond the ball float, that means the refill valve isn’t set properly. You need to recalibrate it.

man repair a toilet that has Fill Valve Fault

How to fix the toilet tank that overfills?

To fix the tank that overfills, you need to stick to the following procedure:

  1. Take off the tank’s lid.
  2. See what kind of overfill mechanism it has. Based on the type of fill valve, you need to make different adjustments.
    1. Sometimes toilets have a float cup connected to the refill tube, squeeze the clip, and lower the water level.
    2. In some cases, you may also find a float arm connected to the refill valve. In that case, locate its screw and make the height adjustment.
    3. Lastly, some toilet tanks also come with a water adjustment rod, you need to configure its position.

Final Words

Toilet problems are often serious and worrisome. But a slight knowledge about the toilets would help you diagnose the root cause of the problem. And there are a few problems that you can fix on your own without needing professional help, such as adjusting the refill tube or the flapper.

So, whenever your double flushes next, you will probably know what’s wrong with it!

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