A toilet keeps running when the water doesn’t fully shut off after a flush, usually because a worn part inside the tank isn’t sealing properly. The most common causes are a worn flapper, a stuck fill valve, a float set too high, or a flush chain that’s tangled or the wrong length.

Most of these fixes take less than thirty minutes and cost less than a service call. A running toilet can waste hundreds of gallons of water a day, so it’s worth tracking down the cause rather than living with the noise. Below, we’ll cover why toilets run, how to stop a toilet from running with a step-by-step fix, and when to call a plumber.

Why Does My Toilet Keep Running?

A toilet tank holds a handful of parts that fill the tank, hold the water, and release it into the bowl when you flush. When one of those parts wears out or shifts out of place, water keeps moving through the toilet instead of shutting off completely. That’s why your toilet keeps running after every flush.

If your toilet is constantly running, it is likely caused by one of the following:

  • Worn or misaligned flapper: The flapper is the rubber piece that seals the bottom of the tank. If it’s warped, cracked, or coated in mineral buildup, it won’t seal, and water slips past it into the bowl.
  • Faulty fill valve: The fill valve controls how water refills the tank after a flush. A worn valve can keep letting water through even after the tank should be full.
  • Float set too high: The float tells the fill valve when to stop. If it’s set too high, water keeps spilling into the overflow tube instead of stopping at the right level.
  • Chain problems: The flush chain (or lift chain) connects the flush handle to the flapper. If it’s too long, too short, or tangled, it can hold the flapper open or keep it from sealing shut.
  • Cracked overflow tube: A crack here lets water leak out slowly. This sometimes causes a “phantom flush,” where the tank refills on its own every so often even though nobody used the toilet.

How Much Water (and Money) a Running Toilet Wastes

A constantly running toilet can waste around 200 gallons of water in a single day. Over a month, that comes out to roughly 6,000 gallons, which is often enough to bump your water bill noticeably. Most fixes cost only a few dollars in parts, so figuring out what’s causing your toilet to run almost always pays for itself fast.

Cause, Fix, and Whether It’s a DIY Job

Cause Likely Fix DIY or Call a Plumber
Worn or misaligned flapper Replace the flapper DIY
Faulty fill valve Replace the fill valve DIY, or call if unsure
Float set too high Adjust the float height DIY
Chain too long, short, or tangled Adjust the chain length DIY
Cracked overflow tube Replace the tube Call a plumber
Cracked tank or porcelain Replace the toilet Call a plumber

How to Fix a Running Toilet (Step-by-Step)

Here’s how to fix a toilet that keeps running, in the order a plumber would typically check things:

  1. Take the lid off the tank and flush the toilet so you can watch what’s happening inside.
  2. Check the flapper. Look for warping, cracks, or a layer of mineral buildup that’s keeping it from sealing.
  3. Adjust or replace the flapper if it isn’t sitting flat or sealing completely.
  4. Check the chain length. It should have a little slack, not be pulled tight or wrapped around itself.
  5. Check the float height. Water should sit about an inch below the top of the overflow tube.
  6. If none of that solves it, inspect the fill valve for wear, cracks, or debris.
  7. Flush one more time and watch closely to confirm the toilet has stopped running.

Fixing a Worn Flapper

Lift the tank lid and flush, then watch what the flapper does. If it doesn’t drop back down flat and seal the drain hole, or if it looks warped or slimy, it needs to come out. Most hardware stores sell universal flappers for under ten dollars, but some toilet brands use a flapper sized specifically for that model, so it helps to check your toilet’s brand and model number before buying a replacement.

Adjusting the Float

Older toilets use a ball float on an arm, while most modern ones use a cup float that rides up and down a rod. A ball float looks like a plastic or metal ball attached to a rod, floating on the water’s surface. A cup float looks like a small cylinder that clips around the fill valve shaft and slides up and down along it. For a ball float, gently bend the metal arm downward to lower the water level. For a cup float, look for a clip or adjustment screw on the fill valve and turn or slide it to lower the float. Either way, aim for a water line about an inch below the overflow tube.

Fixing a Faulty Fill Valve

If adjusting the float doesn’t stop the running, the fill valve itself may be worn out. Shut off the water at the shut-off valve behind the toilet, drain the tank, and unscrew the old valve from the bottom of the tank. A replacement valve usually runs $15 to $25 and comes with instructions for setting the height. This job takes more time than a flapper swap, but most homeowners can still handle it in an afternoon.

Tools You’ll Need to Fix a Running Toilet

  • Work gloves
  • Adjustable wrench or channel locks (needed to replace the fill valve only)
  • Replacement flapper or fill valve kit
  • A sponge or old towel for spills
  • A small bucket to catch water when shutting off the supply

Common Mistakes to Avoid

  • Over-tightening the fill valve or supply line, which can crack the fittings and cause an even bigger leak.
  • Buying a universal flapper when your toilet needs a brand-specific one.
  • Ignoring a toilet that runs quietly. It might seem minor, but it adds up on the water bill month after month.

When to Call a Plumber Instead

Some running toilets need more than a new flapper or valve. If you’ve tried a few fixes and the toilet won’t stop running, or if you notice a cracked tank, cracked porcelain, or water pooling on the floor, it’s time to bring in a professional. Older toilets can also be tricky, since matching parts get harder to find the longer a model has been off the market. In cases like that, replacing the fixture altogether is often simpler than chasing down repairs one part at a time.

At Jennings Plumbing Services, we’re a family-owned company based in Little Elm, and we believe in honest diagnostics and upfront pricing instead of pushing work you don’t need. If a running toilet in your North Texas home turns out to be more than a quick fix, we’ll walk you through your options and let you choose what fits your budget.

Stop the Water Waste — Contact Jennings Plumbing Services

A running toilet is rarely a big problem, but it’s an easy one to fix before it costs you more on your water bill. If you’ve gone through the steps above and the toilet in your Little Elm or North Texas home is still giving you trouble, contact our team, and we’ll take a look, diagnose it honestly, and get it fixed right.