Why Does My Toilet Randomly Runs For A Few Seconds?

Perhaps you have gone to sleep at night, only to be woken by the sound of your toilet casually running! This problem is often referred to by plumbers as a “phantom flush” and sounds like the toilet is flushing itself! Right now, you may be curious as to what causes this to happen in the first place? Well, I have the answer for you below:

Your toilet randomly runs on and off for a few seconds due to a problem called “phantom flush”. This is caused by a slow water leak from the tank into the bowl and is often the result of a sediment build-up on the flapper (aka “flush valve seal”) or a bad flapper seat. This accumulation of minerals from hard water prevents the flapper from sealing completely. If enough water leaks out of the tank, then the refilling mechanism is triggered resulting in a “phantom flush.”
Why Does My Toilet Randomly Runs For A Few Seconds?

Now that you know the main reason why a toilet sometimes runs randomly, let us explore this topic further and in more detail below. We will discuss the common causes as well as how to go about fixing the problem. I will also explain what it means when a toilet continues to run even after the flapper is changed and when you know it is time to call a plumber for help.

So, if you are ready to learn more, then please continue reading…

* This article may contain affiliate links. As an Amazon Associate, I earn from qualifying purchases. 

What Are Common Reasons For A Toilet To Run Randomly?

There are different reasons as to why your toilet is running randomly. The most likely culprit is the flapper not sealing the hole in the tank completely.

As mentioned above, it is usually caused by a build-up of sediment or hard water minerals. Other reasons could include the following:

1. An Improperly Installed Flapper Chain

The flapper chain is what allows the flapper to lift up-and-down as required when the toilet is flushed.

If the chain is not attached correctly (or if it is too long or too short), this can hinder the flapper’s ability to completely seal the hole, thus resulting in a randomly running toilet.

2. A Leak in the Fill Valve

The fill valve is responsible for refilling the tank after the toilet is flushed.

If this valve is damaged or leaking, water will continue to fill-up in the tank, causing the toilet to keep running.

A slow, intermittent leak could be responsible for the toilet running randomly.

3. Not Enough (or Too Much) Water

If the water level in the tank is not accurate, this could cause a toilet to run randomly.

The water should rest 1 to 2 inches (or 2.5 to 5 centimeters) below the fill valve.

If it is higher or lower than this amount, the off-balance will likely result in a ‘phantom flush.’

4. A Faulty Toilet Handle

A handle that sticks or stays down instead of popping back up could also be the culprit.

By not returning to the original position after flushing, the handle can let more water into the tank than necessary.

This can potentially cause the toilet to run randomly.

READ THIS GUIDE: The Anatomy of A Toilet Tank

How Do You Fix a Randomly Running Toilet?

To fix a randomly running toilet yourself, there are 7 steps you need to follow:

  1. Lift the lid of the toilet off and away from the tank.
  2. Lengthen or shorten the lift chain, if necessary. Then, tighten or loosen the chain accordingly so that it has at least ½ inch of slack at the midpoint.
  3. Replace a cracked float ball by turning it counter-clockwise with your hand until it releases from the threaded rod. Next, tighten the new ball securely onto the rod. If the ball seems to be intact but appears loose, simply remove and refasten it.
  4. Adjust the float height properly to ensure the water rises just high enough to shut the fill valve off after flushing. If the float is set too low when it refills, the tank will continue to run.
  5. Clean the flapper thoroughly to remove any sediment build-up. Turn off the water to the tank (usually located on the wall behind the toilet) and then flush the toilet to drain it.
  6. Take an emery board and rub it across the edges of the seat until it is completely free of sediment.
  7. Re-insert the rubber stopper into the seat and turn the water supply to the tank back on.

The above method is a quick and easy way to service a toilet yourself – if you have some basic handyman skills and feel comfortable doing so.

Minor part adjustments and/or cleanings are usually all that is required.

Unless, of course, there is a bigger problem involving a damaged or defective part that needs to be either repaired or replaced.

In which case, it is usually recommended that you hire a professional plumber for the job.

Why Does My Toilet Run after Replacing the Flapper?

A cracked or damaged flapper (or valve seal) is usually the result of a casually running toilet.

However, if you have replaced the flapper and the problem continues, then the flush valve seat is likely the cause and will also need to be replaced.

Or it could be one of the other issues mentioned above.

Will a Randomly Running Toilet Increase Your Water Bill?

The answer to whether (or not) your water bill will increase if you have a randomly running toilet is yes!

A toilet that runs after or between each flush can waste hundreds of gallons of water which would up your plumbing expenses significantly.

Therefore, it is imperative to fix the problem as soon as possible – either by yourself, if you can, or by calling a professional plumber.

Should You Call a Plumber for a Randomly Running Toilet?

As mentioned above, you should call a plumber for a randomly running toilet if you are unsure of the cause or how to fix it yourself.

Be prepared, however, as a professional repair job could cost you $100 to $300, depending on the extent of the problem and the number of parts required to fix it!

Start by contacting different plumbers in your area and getting a few free estimates.

If you have some handyman or plumbing experience, your best bet is to fix it yourself as this could save anywhere from $50 and $200!

On the other hand, if you know nothing about toilets or how to service them, call a professional for help.

Otherwise, you might make the problem worse and the price to repair the damage you have done could be considerably higher than had you just called a plumber in the first place.

What is the Best Toilet Flapper Replacement?

One of the best toilet valve seal replacements is the Korky 100BP Ultra High-Performance Flapper. (Amazon affiliate link)

Its universal design fits most toilets and is easy to install.

It is made from a flexible, long-lasting rubber that creates an ultra-tight seal.

Reasonably priced and readily available, it can be purchased online through Amazon. Check it out today!


To conclude, the most common cause of a randomly running toilet is sediment build-up on the flapper or valve seal.

The accumulation of hard water minerals on this part prevents it from closing completely, which creates a slow leak from the tank into the bowl.

If enough water leaks out, then the refilling mechanism is triggered. This results in what plumbers refer to as a ‘phantom flush.

A toilet that runs intermittently can waste hundreds of gallons of water and could increase your water bill significantly if overlooked or neglected for a long period of time.

Therefore, it is best to fix the problem as soon as possible, either on your own (by following the easy step-by-step instructions outlined above) or by hiring a professional plumber.

Hopefully, this article has been helpful to you. Thanks for reading and good luck fixing your toilet!

Cheers, tools owners!



Hi there! My name is Jack and I write for ToolsOwner. I have a passion for everything related to tools and DIY projects around the house. You often find me in my workshop working on new projects.