Why Your Toilet Keeps Running (And How to Fix It)

It always happens when the house is finally quiet. You’ve brushed your teeth, climbed into bed, and just as you start to drift off—drip… whirr… trickle. That unmistakable sound of your toilet running. Again. 

Besides the sleep disruption, a constantly running toilet is doing real damage where it counts: your water bill. A single running toilet can waste up to 200 gallons per day, which adds up to thousands of gallons (and dollars) over a month. 

The good news? Most running toilet issues are easy to diagnose and often just as easy to fix. In this guide, we’ll show you how to identify the problem, walk through some common DIY solutions, and explain when it might be time to call in a professional. 

The “How-To” Diagnosis 

Before you start replacing parts or adjusting anything, you need to confirm whether the toilet is leaking water from the tank into the bowl. 

The Dye Test 

Here’s a quick and easy method: 

1. Remove the lid from your toilet tank. 
2. Add a few drops of food coloring into the tank (red or blue works best). 
3. Wait about 20–30 minutes without flushing. 
4. Check the toilet bowl. If you see any colored water, you’ve got a leak. 

This tells you that water is moving from the tank into the bowl—even when the toilet isn’t in use. 

Common Culprits and Their Fixes 

Culprit #1: A Faulty Flapper 

The Problem: 

The flapper is the rubber valve at the bottom of the tank. It lifts when you flush and drops back down to seal the tank. Over time, the flapper can warp, crack, or simply wear out, preventing a watertight seal. If the flapper doesn’t seal properly, water can continuously flow into the bowl even if the fill valve is working correctly. 

The Fix: 

1. Turn off the water supply (usually behind the base of the toilet). 
2. Flush the toilet to empty the tank. 
3. Detach the flapper from the chain and the overflow pipe. 
4. Inspect the flapper to see if it is damaged or just needs cleaning. 
5. Take the old flapper to the hardware store to get a matching or universal replacement. 
6. Clip in the new flapper. Make sure the chain has some slack. 
7. Turn the water back on and test. 

This fix is inexpensive and usually solves the problem right away. 

Culprit #2: The Float is Set Too High 

The Problem: 

In a toilet, the float is a device inside the tank that controls the water level. Its job is to signal the fill valve to stop adding water once the tank is full. If the float is set too high, water can spill into the overflow tube, causing the toilet to run continuously. 

The Fix: 

1. Determine your float type: 
   • Ball-and-arm: a long metal or plastic arm with a hollow, round ball on the end. It usually sits on the left side of the tank.  
   • Cup-style: a cylindrical float that slides up and down the vertical shaft of the fill valve. This is usually located toward the back or side of the tank. 
2. Watch It in Action: Flush the toilet and observe the float as the tank refills. The water should stop about 1 inch below the top of the overflow tube. 
   • Make sure the float rises smoothly without sticking or catching.
   • Check function. Once the float reaches the right level, the water should stop automatically. If water keeps spilling into the overflow tube, the float height needs to be adjusted. 
3. Adjust the float: 
   • For a ball-and-arm: Gently bend the arm downward until the water stops overflowing into the tube. 
   • For a cup-style: Use the adjustment screw on the fill valve to lower the float. 
4. Aim for the water level to be about 1 inch below the top of the overflow tube. 

This simple tweak will let the tank fill to the right level and turn off the running water as it should. 

Culprit #3: The Fill Valve is Malfunctioning 

The Problem: 

The fill valve is what refills the tank after each flush. It’s the vertical assembly inside the tank that the float attaches to and controls. Over time, the fill valve can wear out because of mineral buildup, worn seals, or broken internal parts. A malfunctioning fill valve may keep letting water into the tank while the tank is full, causing your toilet to run continuously. Sometimes, issues with the float can make it seem like the fill valve is the problem.  

The Fix: 

 This one is a bit more involved, but it’s still doable for handy homeowners. 

1. Turn off the water supply. 
2. Flush the toilet to empty the tank. 
3. Unscrew and remove the old fill valve. 
4. Install the new valve according to the manufacturer’s instructions. Keep in mind that there are different types of fill valves, so make sure your replacement matches your toilet model. 
5. Turn the water back on and test. Fill the tank and flush a couple of times to ensure the water stops at the correct level and the fill valve shuts off properly. 

If you’re not confident in replacing a fill valve, this is a great time to call in a licensed plumber. 

Culprit #4: The Flapper Chain is Too Tight, Too Loose, or Tangled 

The Problem: 

The chain connects the flush lever to the top of the flapper. If the chain is too tight or tangled, the flapper can’t seal the tank, so water keeps running. On the other hand, a chain that’s too loose can prevent the flapper from fully lifting, leading to weak flushing or a partially-filled tank. 

The Fix: 

1. Remove the tank lid and inspect the chain. 
2. There should be a slight amount of slack when the flapper is down—about ½ to 1 inch of slack is a good rule of thumb 
3. Adjust the chain if needed: 
   • If the chain is too tight, elongate it by moving the hook to a different link. 
   • If the chain is too loose, shorten it by hooking to a different link. ‘
   • Make sure the chain isn’t knotted or catching on any other parts inside the tank. 
4. Test it by flushing the toilet. The flapper should lift and seal properly. 
5. This is one of the easiest fixes on the list, and it can make a surprising difference. 

When to Call a Professional Plumber 

While most running toilet issues are straightforward, there are times when it’s better to let a pro step in. 

The DIY Fixes Don’t Work 

If you’ve tried adjusting the float, replacing the flapper, or checking the chain and your toilet is still running, something more complex might be going on—like a cracked overflow tube or sediment buildup in the valve system. 

The Problem is Beyond Your Comfort Level 

It’s completely okay to stop at any point and call a professional. Your time, tools, and comfort matter. A licensed plumber can resolve the issue quickly and safely, often saving you more time and water than continued DIY efforts. 

Warning Signs to Watch For 

• Cracked or leaking toilet tank 
• Water pooling around the base 
• Corrosion or rust around valve connections 

These could point to problems that go beyond a quick part replacement and may require specialized tools or experience. 

At Wizard Plumbing & Drain, we help Bay Area homeowners fix persistent plumbing issues like running toilets quickly and cleanly. Whether it’s a simple flapper swap or a more complex leak, we’ll get the job done right—so you can get back to sleeping soundly. 

Final Thoughts

If your toilet won’t stop running, it’s likely due to one of a few common causes: a worn flapper that no longer seals properly, a float that’s allowing too much water into the tank, a malfunctioning fill valve, or a flapper chain that’s too tight or tangled. Fortunately, many of these fixes are quick, affordable, and well within reach for most homeowners. 

That said, not every issue is DIY-friendly—and that’s okay. If you’re not confident or the problem isn’t going away, calling a pro can save time, money, and frustration. At the end of the day, stopping a running toilet means saving water, lowering your bills, and restoring peace and quiet to your home. 

If you’re ready to stop the noise and the water waste, call Wizard Plumbing & Drain. We’ll get your toilet back in shape quickly, cleanly, and professionally—so you can finally enjoy some peace and quiet.