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Why Does My Toilet Randomly Run for a Few Seconds?

Why Does My Toilet Randomly Run For a Few Seconds
Written by Kai Michel
Last Update: August 10, 2023

You may have fallen asleep during the night, only to hear your toilet casually running when you wake up. It sounds as though the toilet is flushing itself!

In this case, it is referred to as a “phantom flush” by plumbers. If this has happened to you, you may be wondering what caused it to begin with.

Read on to find out!

Why Does My Toilet Randomly Run for a Few Seconds?

Tools needed to fix the issue

  • Flashlight
  • Gloves
  • Toilet parts (vary based on the reason)
  • Toilet adjustment tools (vary based on the reason)

Reason 1: The toilet flapper has broken

Try shutting off the water supply to the toilet and flushing the toilet if the flapper looks damaged. If there is any leftover water, clean it up with a sponge and attach and replace the flapper. Then turn on the water supply and test it.

The flap has broken when the toilet starts running by itself or the tank fills up. In this case, the lid is not covering the hole in the tank, and the water is escaping, dropping the level.

Solution: Change the flapper

Cracked or worn flappers should be replaced. If your old flapper is broken or damaged, you should bring it to a store that offers repair services.

Overflow pipes typically have flappers mounted on the side lugs. In some cases, the replacement flapper will have a molded or plastic ring between the arms that must be removed or cut away. Then, slowly turn on the water again.

Reason 2: The flush handle does not return to its original position

Handles that stick or stay down instead of rising automatically may also be blamed.

The handle should return to its original position when flushed. If this fails, too much water can enter the tank.

This may result in the toilet running.

Solution: Check the handle after flushing

After you have flushed, check the handle. If it isn’t returning to the original position, try spraying with WD-40. It may need some lubricant.

If this still doesn’t work, check the lever arm. It may be bent or need repairing. If the handle appears to be going up less and less to the original position it will need replacing.

Reason 3: The refill tube positioning is incorrect

Water is pumped into the bowl. If the refill tube is too long or not positioned correctly, it will continually run. Fill valves create a suction effect that draws water from the fill valves into the toilet. As a result, you need to shorten the tube or position it directly over the overflow opening.

Solution: Look at the refill tube, float, and ballcock or inlet-valve assembly

Check if anything has come apart, has broken, or seems abnormal.

Reason 4: Damage to the fill valve

After flushing the toilet, the fill valve refills the tank.

If the valve has become damaged or has a leak, the toilet will continue running if the water in the tank fills up.

Solution: Replace the fill valve

You can test whether your fill valve is causing your leaky toilet by adding food coloring to your tank. Check to see if the water in the bowl is the same color when no one has flushed the toilet. If it is leaking, the best solution is to get a replacement.

Reason 5: The tank float is too high

When there is too much water in the tank, toilets can overflow or run continuously. If the float has become too high, too much water will fill up in the overflow tube, causing it to overflow.

If the toilet runs intermittently due to too much water in the tank, the float needs to be lowered to prevent the tank from filling up too fast.

Solution: Adjust the float height

A simple change of the float height may be all that you need if your flat ball doesn’t leak. It’s very easy to do.

Unfortunately, if the float doesn’t reach the fill level, the valve won’t shut off. So when the tank is bobbing back and forth, it can cause it to run.

After installing a metal ball float in place of plastic, your ball float could rise. Then, when you compress the spring clip, you can adjust the float by sliding it up or down.

If your toilet has a rubber ball, a metal arm should be visible. Set the screw on the arm end to a different position, or if the screw isn’t visible, bend the arm.

Reason 6: The flapper chain is too short

The flapper will become raised and lowered by the flapper chain as the toilet flushes. If the chain isn’t attached correctly or is the incorrect size, you will face problems. It can prevent the flapper from sealing completely, causing the toilet to run.

Solution: Check the lift chain

You could potentially stop the toilet from running by lengthening the lift chain. A rubber disk on the bottom of your tank connects to the lift chain at the back of the handle.

A flapper is a rubber disk. A chain that is too short may cause the flapper to not seal since the chain will pull the flapper upward.

You should adjust the chain to have around 1/2 inch of slack around the center. You can adjust the chain by disconnecting it from the handle, then reattaching it to the following link.

Reason 7: Leaky seals

People think the seat and the tank share a single seal. Well, that’s not true. 9 out of 10 toilets have 5 seals. This means that there are five possible leak points. In the event of a leak, the seal that’s between the bowl and the tank is damaged.

Solution: Replace the float ball

There may be a leak in your toilet float ball. To fix it, simply replace the ball. A rubber or metal ball inside your toilet tank is known as a float ball. It should hover above the water.

The ball will sink a bit if it is leaking. The toilet will run. Remove the rod from the ball and turn it in the opposite direction to fix the problem. Replace the old float ball with a new one. Tighten the float ball clockwise.

Reason 8: Defective sensor

In high-tech toilets, cleaning and flushing get controlled by many sensors. If one of the sensors isn’t working as it should, your toilet will run for a few seconds randomly.

Solution: Fix or replace the sensor

The sensor may need refitting or completely replaced while obstructions can cause the sensor to malfunction . Depending on the design of your toilet, you may need help to repair and or replace the sensor.

Reason 9: No vent pipes

When water flows down the pipe, it creates a vacuum that draws water out of your toilet and p-traps. Sink and bathtub drains usually emit an unpleasant odor when that happens.

Solution: Install a vent under your sink

The lack of vent pipes can cause this. If the water flowing down your pipe creates a vacuum, the water can be drawn out of your p-trap and toilet. Sink and bathtub drains usually start smelling if that happens.

Reason 10: The nut holding the flapper unit to the tank is loose

This is quite a common problem. The plastic nut that attaches to the flapper unit to the tank wasn’t tight enough. This allows water to slowly seep out.

Solution: Check the lift chain

The fix is the same as Reason 6 mentioned above – too short flapper chain.

Reason 11: Weakened gasket

The toilet tank bottom is where the gasket gets attached. This determines when to release and when to contain water. So, it plays an important role in water management.

If not replaced, it will become damaged and leak water in the long run. Consequently, the toilet will run.

Solution: Fix or replace the gasket

Water and sewer gas cannot escape from your toilet as the gasket creates an airtight seal. If the wax ring becomes damaged, it needs replacing immediately to prevent leaks.

Reason 12: A build-up of sediment on the flapper

The most common reason for toilets to flush randomly is when the flapper has become damaged. It can also occur when sediment has accumulated on the flapper/tank. This prevents the flapper from making a complete seal.

Solution: Clean the valve seat

The second option is to clean the valve seat as part of a regular maintenance plan. Make sure you remove sediment deposits.

A metal valve seat is compatible with older models. You can also find a triangle-shaped rubber stopper on the tank’s bottom. In the case of a broken or incomplete seal, it might occasionally run.

You can now use a nail file or emery board to remove the rubber stopper from the valve seat. Use this to scrub any deposits from the valve seat. Put the rubber stop back in its place and turn on the water once you’re finished.

Reason 13: Water drips out from the top of the tank

Solution: Increase or decrease the level of water in the tank

Float rods can bend up or down to change the level of water in the tank. However, overflow tubes must be below the water level in the tank. If not, adjust them until you reach the desired level.

Reason 14: Low or fluctuating water pressure

Solution: Fix a pressure reducing valve (Not matched with a problem)

If your toilet is running, you may need a plumber to replace the pressure reducer valve. In some cases, the water pressure inside the house may need adjusting.

When to call a professional plumber to fix the issue?

If you have tried the above solutions to no avail, think about professional help. Call a plumber if you don’t have the skills to attempt a DIY repair for avoiding further damage happening to the toilet.


Q. 1: Will a randomly running toilet increase my water bill?

Ans. Yes, it can! The cost of running a toilet after and between flushes could be hundreds of gallons. It can increase your plumbing costs.

As a result, it is crucial to solving the problem right away – either by yourself, if possible, or by hiring a plumber.

Q. 2: Is it normal for my toilet to run after I replace the flapper?

Ans. Flappers (or valve seals) that have cracks or damage usually result from a running toilet. If problems persist after replacing the flapper, the flush valve seat needs replacing.

Q. 3: Every time I use the toilet, there is a noise. Why is that?

Ans. This sound can appear every few minutes or once in a while. A toilet refill sound usually signals that water is leaking on the inside or exterior of the toilet.

Q. 4: Can a running toilet cause a flood?

Ans. Running toilets can become flooded toilets. The excess water can flood your septic tank. This can cause your drain field to become saturated and fail.

About the author

Kai Michel

Hello, this is Kai, addressing homeowners in need of some help with their home renovation projects. I’ve worked on numerous toilet repair projects over the years that incorporated a wide variety of tasks, from repair to renovation and maintenance. Besides acquiring a degree on the legal codes and procedures, I gathered vast insights into bathroom settings, toilets, showers, fittings, and other household appliances, fixtures, and components. This helps me guide my clients through their home improvement and interior development plans. Since maintenance is my area of expertise, I can assist people in all phases of the actual ‘improvement’ process. To get my messages even further, I contribute to this site through my blog posts. Check my content here for expert suggestions!

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