Why Is My Toilet Constantly Running? Causes, Fixes, and What It's Costing You

That sound of water trickling after you flush — and then just continuing — is easy to ignore. But a constantly running toilet is costing you real money every day, and in most cases it is one of the simplest plumbing problems to fix.

Here is what is probably causing it, how to check, and when you need a plumber versus a $10 trip to the hardware store.

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What a Running Toilet Actually Costs You

Before we get to the causes, here is why this matters beyond just the noise.

The EPA and multiple water utilities cite a medium toilet leak as wasting roughly 200 gallons of water per day. Over a year, that adds up to more than 70,000 gallons. At average US water rates, that translates to roughly $240 to $360 per year in wasted water costs — sometimes more depending on where you live, per Trident Plumbing.

The fix often costs $5 in parts and 15 minutes of your time. The math makes it one of the most worthwhile home repairs you can do.

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How a Toilet Tank Works (in 30 Seconds)

Understanding the cause requires knowing three parts:

• Flapper: A rubber seal at the bottom of the tank. After you flush, it drops back down and seals the tank so it can refill.
• Fill valve (ballcock): Controls water flowing into the tank after a flush. Shuts off when the water reaches the correct level.
• Float: A ball or cup that rises with the water level and signals the fill valve to stop.

When any of these three fails, water either constantly drains from the tank into the bowl, or the fill valve never shuts off.

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The 4 Most Common Causes

Cause 1: Worn or Warped Flapper

This is the most common cause of a running toilet by a wide margin, per Benjamin Franklin Plumbing and Kohler. Rubber flappers dry out, warp, or accumulate mineral deposits over time, and stop creating a watertight seal. Water slowly drains from the tank into the bowl continuously.

Test: Put 5–10 drops of food coloring into the tank. Wait 15–20 minutes without flushing. If color appears in the bowl, your flapper is leaking.

Fix: Replace the flapper. A universal flapper costs $5 to $15 at any hardware store. Replacement takes about 10–15 minutes — turn off the supply valve, flush to empty the tank, unhook the old flapper, snap in the new one.

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Cause 2: Float Set Too High

If the float is positioned too high, the water level in the tank rises above the overflow tube — a vertical tube in the center of the tank — and water constantly drains down it into the bowl. You can usually see this by removing the tank lid and observing water running over the top of the overflow tube.

Fix: Adjust the float height downward. On older ball-float systems, bend the float arm slightly downward. On newer cup floats, there is typically an adjustment screw or clip. The water level should sit about 1 inch below the top of the overflow tube.

Cost: Free — no parts needed in most cases.

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Cause 3: Faulty Fill Valve

If the fill valve does not shut off properly, water continuously runs into the tank and out through the overflow tube. You can hear this as a constant hissing sound from the tank.

Fix: Fill valves can sometimes be adjusted, but if worn, replacement is the more reliable fix. A new fill valve costs $10 to $20 and installation is a moderate DIY task (requires turning off supply and draining the tank). If you are not comfortable with it, a plumber can replace one in under an hour.

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Cause 4: Flapper Chain Too Short or Tangled

A chain that is too short prevents the flapper from dropping all the way down after a flush, leaving a small gap that lets water trickle through continuously. A chain that is too long can get caught under the flapper, causing the same problem.

Fix: Adjust the chain length so there is about ½ inch of slack — enough to allow the flapper to close fully but not so much that it tangles.

Cost: Free.

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DIY vs. Calling a Plumber

Situation	DIY or Plumber?
Flapper needs replacing	DIY — $5–$15 in parts
Float adjustment needed	DIY — free
Chain adjustment	DIY — free
Fill valve replacement	DIY if comfortable; plumber if not
Problem persists after above fixes	Call a plumber
Toilet is cracked or seal at base is leaking	Call a plumber

Professional repair cost: Most plumbers can resolve a running toilet in under an hour. Expect to pay $150 to $300 for a standard toilet repair, or up to $200 to $500 for more complex issues, per multiple plumbing sources.

You will recover the plumber's fee in water bill savings within the first year in most cases.

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When to Call a Licensed Plumber

Call a plumber when:

• You have replaced the flapper, adjusted the float, and checked the chain — and the toilet is still running.
• The fill valve replacement is beyond your comfort level (the supply connection involves fittings that can crack if overtightened).
• Water is leaking at the base of the toilet or from the tank-to-bowl connection — this suggests different issues like a failed wax ring or tank bolts.
• The toilet is old enough that multiple components are failing at once — at that point, a full toilet replacement may be more cost-effective than continued repairs.

Find a licensed plumber near you for toilet repair in your area.

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Key Takeaways

• A running toilet wastes approximately 200 gallons per day (medium leak) — costing $240 to $360 per year in wasted water.
• The most common cause is a worn flapper — a $5–$15 part that most homeowners can replace themselves in 15 minutes.
• Other common causes: float set too high, faulty fill valve, tangled flapper chain.
• Food coloring test: Drop dye in the tank, wait 20 minutes — color in the bowl means the flapper is leaking.
• Professional toilet repair typically costs $150 to $300 and pays for itself in water savings within a year.