Why Does My Toilet Keep Running? 7 Causes and When to Call a Plumber

Nothing is worse than having your toilet keep running after you flush – or periodically start running on its own. It’s more than just an annoying running sound that requires someone to get up and “jiggle the handle” and hopefully get the running to stop. A toilet that doesn’t shut off properly can waste hundreds of gallons of water, increase your utility bill, and may be a sign that a component inside the tank needs attention.

The good news? Many running toilets have a relatively simple cause due to an internal water leak in the toilet. But if you’ve checked the obvious culprits and the toilet still won’t stop running, it may be time to call a professional plumber. The licensed, professional Denver plumbers at Bell Plumbing, Heating, Cooling & Electrical are standing by to help!

Here are seven common reasons your toilet keeps running – and what you can do about them.

1. The “Toilet Flapper” Isn’t Sealing Properly

The toilet flapper is a common culprit for running toilets. These flaps are a watertight seal for your toilet’s water tank. As they age, they can decay, crack, or become covered with mineral buildup. When this happens, the toilet flapper, which is supposed to raise the lift arm in the tank by pulling on a chain attached to the toilet flapper, has a hard time raising so water can fill the toilet bowl. When the flapper fails to drop back into position to seal the tank, water slowly leaks from the tank into the bowl, causing the toilet to periodically refill.

What to check:

With the tank lid removed, watch what happens after you flush. Does the flapper settle into place but continue allowing water to leak into the bowl? You can also add a few drops of food coloring to the tank. Wait about 15 minutes without flushing. If colored water appears in the bowl, the tank is leaking.

How to fix it:

If the toilet flapper is clearly a little worse for wear, you can try replacing it yourself. They are available at your local hardware store. You have to turn off the water supply on the valves beneath the toilet, flush, and then remove leftover water in the bowl. You can then unhook the flapper and attach the new one.

2. The Toilet Chain Is Too Loose – Or Too Tight

If the flapper seems fine, it could be the chain attached to the flapper causing the issue. In some cases, the chain length can make it hard for the flapper to connect fully to seal the tank. When it’s too long, it gets caught beneath the flapper. When it’s too short, it can prevent the flapper from fully closing. Either situation can keep your toilet from flushing or sealing correctly.

What to check:

Look inside the tank while operating the handle. The chain should have a little slack when the flapper is closed, but not so much that it gets tangled or caught underneath the flapper.

How to fix it:

Try unhooking the chain and re-hooking it so it’s the right length. You’ll have to do a test flush to make sure you get it in the ideal spot because if you miss the mark, the seal won’t work at all.

3. The Float Is Set Too High

Your toilet's float helps control the water level inside the tank. When the water reaches the appropriate level, the fill valve should shut off. If the float is set too high, the tank can overfill. Water may run continuously into the overflow tube, creating the familiar sound of a toilet that won't stop running.

What to check:

Lift the lid from the toilet tank and observe the water level. The plastic ball is attached to an arm, and together they rise and fall as water empties and refills in the tank. Its purpose is to help monitor water levels, and when the ball reaches a certain level, the water stops running. To see if it’s working properly, you need to lift the float arm and see if that stops the running water.

How to fix it:

If the ball isn’t high enough to stop the running water, it might be hitting the tank because the arm is off-kilter. You can bend it away from the tank wall and see if this helps. If it appears the ball and arm are aligned, then the ball might be cracked, which will cause it to fill with water and sink to the bottom of the tank. When this happens, the water keeps running because the ball isn’t reaching its proper position to stop it. All that water feeds into an overflow tube and just keeps running. This simple fix is to replace the float ball. If adjusting the float doesn’t solve the problem, the fill valve may need attention.

4. The Fill Valve Is Worn Out

The Fill valve controls the flow of fresh water into your toilet tank after you flush. Over time, the valve can wear out or become affected by mineral deposits. When that happens, it may fail to shut off completely—even when the tank has reached the proper water level.

What to check:

Listen for constant hissing or trickling sounds coming from the tank. Watch for signs the tank is taking a long time to fill. Check for intermittent refilling, where the toilet randomly turns on by itself for a few seconds.

How to fix it:

A faulty fill valve typically needs to be cleaned, adjusted, or replaced. If you're comfortable working inside the toilet tank, replacement may be a manageable DIY project. Otherwise, a Bell, licensed plumber can quickly diagnose the problem and replace the component if necessary.

5. The Flush Valve Or Other Internal Components Are Damaged

Depending on the age and design of your toilet, other components—including the flush valve, seal, or overflow tube—can become damaged or deteriorate over time. Older toilets may have multiple worn components at once.

Why this matters:

Replacing one part may temporarily improve the problem without addressing the underlying issue. If several components are deteriorating, it may make more sense to have a Bell Denver plumber evaluate the entire toilet. Our professional plumbers can determine whether a repair is appropriate—or whether replacing the toilet would be the better long-term solution.

6. Mineral Buildup Is Interfering With The Toilet’s Operation

Colorado’s water can contain minerals that gradually accumulate inside plumbing fixtures. Mineral deposits can interfere with valves, seals, and other moving parts inside your toilet. They can also prevent components from creating a proper seal. If your toilet is older or you're noticing buildup around other plumbing fixtures in your home, mineral deposits may be contributing to the problem.

How to fix it:

Some buildup can be cleaned away, but heavily affected components may need to be replaced. If mineral buildup is causing recurring plumbing problems throughout your home, a licensed Denver plumber can also help you determine whether whole-home water treatment makes sense for your household.

7. There Could Be A Problem You Can’t See Inside The Tank

A toilet may run because of a worn internal component, an improperly adjusted mechanism, a damaged seal, or another issue that isn't apparent from a quick inspection. A toilet that repeatedly cycles on and off may be losing water slowly, even when no one is using it, and shouldn’t be ignored.

If you’ve checked the toilet flapper and replaced it, and adjusted the float arm or replaced the float ball, and you still have that annoying running water sound, things are a little worse. Your last hope is that the entire ballcock assembly has to be replaced. You can head to the hardware store to find a ballcock assembly kit, which usually provides instructions to help the DIYer do the installation themselves. However, this gets a little more complicated and might be best left to the professionals at Bell Plumbing, Heating, Cooling & Electrical. Also, should you do all of these steps, including a complete replacement of the ballcock assembly, and the toilet still runs, you might need a new toilet.

Get Help from Denver’s Toilet Repair Pros!

This is where we come in. As your Denver plumber, we can quickly rid you of that annoying running water sound and save you money on water wastage. Give us a call today!

Call (303) 731-5469