Why Your Toilet Randomly Runs | How To Fix It

A toilet randomly running for a few seconds or one that runs non-stop are common problems that many homeowners face. Fortunately, these issues are easy to fix and usually don’t require the assistance of a plumber to do so. 

The problem is caused by a malfunction in one of three areas: the fill valve and float, the flapper or flapper chain, or the fill tube. Checking these parts for wear or damage will often reveal the reason why your toilet randomly runs for a few seconds or why it won’t stop running.  

A leaky toilet is wasteful. Even a minor leak can waste as much as 72,000 gallons of water a year, making your annual water bill much higher than it needs to be. If you are dealing with an intermittently running toilet, use the advice below to fix it A.S.A.P. to save yourself some money and help the planet to boot. 

Is Your Toilet Running When It Shouldn’t

The first thing you need to do if your toilet runs when it shouldn’t is to figure out how it is running. Is it running continuously after you flush it, or does it randomly run for a few seconds here and there? 

Toilet Keeps on Running After the Flush

When you flush the toilet, the water should run long enough to fill the bowl and tank and then shut off. Sometimes, however, a significant leak or malfunctioning part causes the toilet to continue running well after the bowl and tank are full. If you have ever had to “jiggle the handle” to get your toilet to stop running after flushing, you have a non-stop running toilet. 

Toilet Runs Occasionally for a Few Seconds

A toilet randomly runs when a minor leak is happening or one of its main parts isn’t working as it should. You might be sitting in your living room watching TV and hear the toilet down the hall run for a few seconds and then shut off again. If you’ve ever gotten up to investigate the running water sound only to hear it stop as soon as you walk into the bathroom, your toilet is intermittently running.

You may also find this article helpful How To Fix A Toilet That Keeps Flushing Itself

5 Reasons Your Toilet Runs Randomly

There are several reasons your toilet is running randomly, and I’ve explained them below in order of them being the probable cause. It’s common to have issues with a flapper chain or seal, as these can get caught or worn over time. So let’s start right there…

1. Flapper Chain Getting Caught or Too Short

When you flush a toilet, the handle on the outside pulls a chain inside the tank to lift the flapper, which begins the flushing process. The chain must have enough slack in it to allow the flapper to seat correctly so that the bowl stops filling, and the tank can begin to fill. 

If the chain gets caught on something inside the tank or is shorter than it needs to be, it can stop the flapper from closing and sealing properly, resulting in water leaking into the toilet bowl. This type of leak can cause a toilet to run randomly as the toilet attempts to keep the tank full. 

2. Damaged Toilet Flapper or Seal

If the flapper chain is long enough and the flapper seats properly in your toilet, the problem may be the flapper itself. Because the flapper is immersed in water, it can deteriorate over time. It can also become caked with mold, mildew, and/or hard water buildup, which can keep it from sealing properly to the bottom of the toilet. 

3: Ball Float Needs Adjusting

The ball float is what tells the toilet how high to fill the water. If the float is positioned too high in the tank, the water will fill too high and spill over into the overflow tube. This can cause the toilet to overflow or run intermittently as it tries to keep the tank water full. 

4. Faulty Flush Mechanism

Sometimes, the flush handle can become loose. This can cause the flapper chain and/or flapper to not function properly. Further, if your toilet has a flush button, it’s possible for the button to fail, which can cause the toilet to leak, flush slowly, or even not flush at all.

5. Refill Tube Need Repositioning

The refill tube is what carries water from the tank into the bowl. If it isn’t positioned just above the overflow opening, it can allow water to continually flow into the toilet bowl. A fill tube that’s too long can also cause intermittent toilet running, too. 

You may also be interested in 4 Reasons Your Toilet Takes So Long To Fill

How To Fix A Toilet That Randomly Runs

Now that you know what causes a randomly running toilet and have identified the cause, it’s time to fix it. Like I said before, the solution to your running toilet problem is an easy DIY project, so keep reading to find out what to do. 

Check the Flapper Chain Length

  • Remove the cover from the toilet tank
  • Locate the flapper chain and watch it as you flush the toilet
  • If the chain is getting caught or is otherwise too short to allow the flapper to close properly, make the necessary adjustments so that the flapper closes as it should.

Replace the Flapper and Seal

  • Turn off the water valve behind the toilet
  • Remove the tank cover and flush the toilet to drain the water. Use a sponge to sop up any water that remains 
  • Unlock the old flapper and replace it with a new one
  • Turn the water back on and do a flush test

Toilet Keeps Running After Replacing the Flapper?

If your toilet keeps running after replacing the flapper, it could be that mineral deposits have built up on the bottom of the tank and won’t allow the new flapper to seal properly.

Clean Mineral Build-Up Around Seal

  • Remove the cover from the tank
  • Pour white vinegar into the tank water to about an inch below the top
  • Allow the water-vinegar solution to stand for 12 hours or overnight to dissolve the rust and mineral buildup
  • Flush the toilet twice and then turn the water off
  • Flush the toilet again to remove the water from the tank
  • Use a scrub brush to remove any remaining buildup from the bottom of the tank
  • Turn the water back on and flush the toilet a couple of times to get rid of unsightly gunk and bits floating in the water
  • Repeat as necessary until the flapper seals correctly and the toilet stops running when it shouldn’t. 

Adjust Ball Float in Tank

  • Take the tank cover off
  • Locate the ball float and do a test flush to see how high the water rises
  • If the float is allowing the water to rise too high, adjust the float arm lower by turning the screw on the arm. 
  • After adjusting the ball float lower, make sure the chain is the right length. If it’s too long, shorten it enough that it doesn’t catch on anything and the flapper functions correctly

Adjust the Flush Mechanism

  • Remove the tank cover
  • Locate the flushing mechanism. If it is loose, tighten the nut counterclockwise until the handle tightens and lifts the flapper properly when flushed

Shorten Refill Tube

  • Open the toilet tank
  • Find the refill tube – it’s the small plastic tube running from the tank’s fill valve to the overflow tube
  • If the end of the tube is underwater, use a pair of cutting pliers to cut it back so the end is no longer under the water level

Call a Plumbing Professional

If the fixes above fail to address your toilet running issue, or if you just don’t feel comfortable tackling the repair yourself, don’t hesitate to call a reputable plumbing professional in your area. Allowing a toilet to randomly run, even just a few times each day, can waste gallons of water and raise your water bill by hundreds of dollars a year. 

You may also like to read Why Is My Toilet Backing Up Into The Shower

SOLVED: Toilet Running Randomly

A toilet running randomly is a common problem in many households. Luckily, the issue is easy to fix yourself by figuring out why your toilet is running and then using the step-by-step instructions above. Fix the issue as soon as possible to avoid throwing money down the drain – literally!

FAQs Toilet Randomly Runs

Still, have questions about your randomly running toilet?

Plumber and HVAC Technician | Website | + posts

As a retired Master Plumber Jamie has over 30 years of hands-on experience, making his plumbing knowledge second to none. He has also worked on both residential and commercial HVAC installation and repair projects.