What Is the Most Common Cause of a Running Toilet?

A running toilet might seem like a small issue, but it can waste gallons of water every day and slowly increase your monthly water bill. Even if it’s just a faint trickle or the occasional sound of water refilling, those little drips add up over time. The good news? Most running toilets are caused by one simple issue you can often fix yourself.

In this blog, we’ll walk you through the most common cause of a running toilet, other possible issues to look for, how to troubleshoot, and when it’s time to call in a professional plumber.

In nearly every case, a running toilet is caused by one thing: a faulty toilet flapper.

The toilet flapper is the rubber (or sometimes plastic) valve at the bottom of your tank. It opens when you flush, allowing water to exit the tank and rush into the bowl. Once the flush is complete, the flapper is supposed to close tightly to allow the tank to refill and hold water until the next flush.

What Goes Wrong with the Flapper?

• Rubber wears down: Over time, rubber can harden, crack, or warp, which prevents it from sealing the drain.
• Build-up of minerals: Hard water can leave calcium or lime deposits that interfere with the seal.
• Chain problems: If the chain is too tight, it may prevent the flapper from closing. If it’s too loose, the flapper may not lift properly.
• Misalignment: Even a small shift in positioning can cause the flapper to stay slightly open.

Signs Your Flapper Is the Problem:

• The toilet sounds like it’s constantly trickling water.
• You have to jiggle the handle to stop the running.
• Water level in the tank slowly drops even when not in use.
• Toilet refills randomly when no one has used it.



How to Fix It:

Replacing the flapper is usually the easiest and cheapest fix for a running toilet. Most models cost under $10 and can be installed in under 10 minutes. Just make sure you get the right size and style for your toilet.

Pro Tip: Take the old flapper to the hardware store or match the brand to get the right replacement.

Why a Running Toilet Matters

If your toilet keeps running long after you flush or starts refilling randomly in the middle of the night, you’re dealing with a running toilet. And while it may not seem urgent, this type of problem can lead to:



• High water bills: Just one running toilet can waste up to 200 gallons of water per day.
• Environmental waste: Wasting water puts unnecessary strain on local water supplies.
• Hidden damage: In rare cases, leaks from the tank can affect flooring or cause mildew around the toilet base.

Running toilets are usually easy to fix, so there’s no reason to wait.

Other Reasons Your Toilet Might Be Running

While the flapper is the most common issue, it’s not the only one. If replacing the flapper doesn’t solve the problem, consider these other possibilities:

1. Faulty Fill Valve

The fill valve controls the water that enters your tank after a flush. If it doesn’t shut off completely, water will continue to flow, causing the toilet to run endlessly. You may hear a faint hissing or see water constantly moving.

Fix: Adjust the valve float height or replace the fill valve if it’s worn out.

2. Float Set Too High

The float is the part that rises with the water level and signals the valve to shut off. If it’s set too high, the water may rise above the overflow tube and cause constant refilling.

Fix: Adjust the float level so that it stops filling about 1 inch below the top of the overflow tube.

3. Overflow Tube Issues

The overflow tube prevents your tank from overflowing. If water is spilling into this tube continuously, that’s a sign your water level is too high or your fill valve isn’t working correctly.

4. Flush Valve Seat Damage

If the surface where the flapper sits is cracked, corroded, or worn down, it may not seal properly even with a new flapper.

Fix: Inspect the valve seat and replace the entire flush valve if necessary.

How to Troubleshoot a Running Toilet

If you want to confirm what’s causing the issue, try this simple test:



1. Remove the tank lid.
2. Add several drops of food coloring to the water in the tank (do not flush).
3. Wait 15 to 30 minutes.
4. If the colored water appears in the toilet bowl without flushing, your flapper is leaking.

Also, listen closely. If you hear a continuous hiss or trickle, it’s likely a problem with the fill valve or flapper. Watch the water level and observe if it rises into the overflow tube.

When to Call a Professional Plumber

While many running toilet issues are DIY-friendly, not all are. If you’ve tried replacing the flapper and adjusting the float and the problem continues, you may need help.

Call a plumber if:

• You suspect a leak under the toilet or around the base
• Parts inside the tank are corroded or broken
• Your toilet is an older model with hard-to-find replacement parts
• You want to upgrade to a more efficient toilet

At Quality Plumbing Heating Cooling & Electrical we offer full toilet repair and replacement services. Our plumbers serve Kodak, Morristown, and nearby communities in Tennessee with trusted, efficient service. We can even do a full video camera inspection to make sure there are no hidden issues in your plumbing system.

FAQs About Running Toilets

How much water does a running toilet waste?

A single running toilet can waste between 100 to 200 gallons of water per day, depending on the severity of the leak.

How much does it cost to fix a running toilet?

If you do it yourself, the cost may be under $10. A plumber may charge anywhere from $75 to $200 depending on what needs to be repaired.

How long does it take to fix?

Most DIY fixes take under 15 minutes. A professional can typically fix a running toilet in one quick visit.

Should I shut off water to a running toilet?

Yes. If the toilet won’t stop running and you’re concerned about wasting water, turn the valve behind the toilet clockwise to shut off the water.

Can a running toilet damage my home?

While rare, a leak from the tank or base could eventually damage flooring or subflooring if not addressed.

Don’t Ignore a Running Toilet

A running toilet may not seem like an emergency, but ignoring it can lead to high water bills, wasted resources, and annoying nighttime noise. The most common cause is usually simple—a worn-out flapper that needs replacing. But if the issue is more complex, we’re here to help.

Our team at Quality Plumbing Heating Cooling & Electrical has the tools and expertise to fix your running toilet fast. Whether it’s a simple flapper swap or a full toilet replacement, we’ve got you covered.

Contact us today for certified plumbing services!