Your toilet won’t stop running. Let’s find out why.

Symptom Selector

What is your toilet doing right now? Pick the behavior that matches, and we’ll point you to the fix.

• Runs constantly: Water escaping into the bowl nonstop, most often from a worn flapper. A faint, steady trickle hours after the last flush is the giveaway. We’ll route you straight to the Flapper Problems section below.
• Runs intermittently: Short bursts of running with no flush in between usually mean a slow leak or a fill valve that can’t hold a seal. We’ll send you to our Toilet Why does my toilet keep running breakdown to narrow it down.
• Won’t stop after flushing: If the tank keeps refilling past the point it should shut off, that’s a classic fill valve symptom. We’ll take you to the Fill Valve section below.
• Makes noise: Whining, hissing, or humming after the tank fills traces to fill valve wear or water pressure. A sharp whine often means a worn washer; a low hum or chatter can mean pressure higher than the valve is rated for. We’ll link you to our full guide, Why Does My Toilet Keep Running? (7 Causes), to match the sound to the cause.
• Phantom flushes: Your toilet flushing itself with nobody touching it is almost always a slow leak past the flapper. We’ll send you to How to replace a flapper for the full explanation.
• Water level looks off: Bowl water lower than usual, or tank water below the fill line, is often a clue pointing to the same flapper or fill valve issues rather than a separate problem.
• Toilet is clogged, not running: A blockage is a different problem. Our guide on how to unclog a toilet without a plunger covers that scenario.

Why This Happens

Most of the time, the cause of a running toilet is either a faulty flapper or the fill valve. Your toilet has two main jobs: the flapper holds tank water until you flush, and the fill valve refills the tank afterward. If the flapper leaks, the fill valve repeatedly tops off the tank. If the fill valve does not shut off, water spills into the overflow tube continuously.

Flapper Problems

The #1 Reason Toilets Run: A Worn Flapper

If your toilet runs constantly, meaning you can hear or see water moving even when nobody’s flushed, the flapper is the first thing to check. Most of the time, it’s the flapper. It’s the rubber seal at the bottom of the tank that lifts when you flush and drops back to seal the tank from the bowl. When it wears out or stops sitting flat, water slowly leaks past it into the bowl, and the fill valve keeps topping off the tank to compensate. That’s the running sound you’re hearing.

A worn flapper usually looks the part: stiff, brittle, or slightly gummy rubber, with mineral buildup or a warped edge where it no longer sits flush. Chlorine tablets and bowl cleaners dropped directly in the tank speed this up. They’re hard on rubber. If your toilet is 2-3 years old or older and uses in-tank cleaning tabs, a degraded flapper should be your prime suspect.

Sub-Symptoms That Point Specifically to the Flapper

• Chain too long or tangled lets the flapper drop crooked; too little slack holds it slightly open. Aim for a half-inch of slack.
• Flapper looks fine but still leaks if it’s warped just enough to break the seal without visible cracking. Any stiffness along the edge is enough to cause a leak.
• Mineral buildup on the valve seat, not the flapper, can keep even a new flapper from sealing. Wipe the seat with vinegar before assuming the part is defective.
• Flush handle sticking can hold the flapper open a crack, a linkage issue, not a flapper issue.

Fill Valve

When the Fill Valve Is the Problem

Odds are, if the flapper isn’t the problem, the fill valve more than likely is. If your toilet runs right after you flush and just won’t shut off (or you hear hissing or a slow trickle minutes after the tank should be full), the fill valve is the more likely cause. It’s the taller mechanism on the left side of the tank that controls how much water comes in and when it stops. When its seal wears out or the float is set wrong, it can’t sense when to shut off, so it keeps feeding water, sometimes straight into the overflow tube where you’ll never notice unless you lift the lid.

Why Fill Valves Fail

Inside every fill valve is a small rubber or silicone seal that opens to let water in and closes when the float signals the tank is full. Mineral deposits from hard water build up on this seal over time, keeping it from closing fully. The problem usually starts as a faint hiss that gets louder over months. Most fill valves are rated for 5-7 years; harder water or higher pressure often means failures closer to 4-5 years.

Diagnosing the Fill Valve vs. Other Causes

Lift the tank lid and watch what happens after a flush.

• Water trickling into the overflow tube after the tank looks full and the flapper has sealed, the clearest fill valve signature.
• Hissing that continues more than a minute after refill. The internal seal isn’t closing fully.
• Float stuck, waterlogged, or set too high. Older ball floats crack and fill with water, becoming too heavy to trigger shutoff; newer cup floats stick from mineral buildup. Lift the float by hand. If water shuts off immediately, that’s the issue, not the seal.
• Water spraying unevenly inside the tank points to a cracked valve cap, usually meaning full replacement.
• Occasional running after a normal refill can mean pressure spikes at certain times of day, making the valve chatter even when it isn’t worn.

For a step-by-step on replacing the fill valve, click here or download HomeFlash. Will tell you what’s failing with the flash of a camera.

When to Call a Pro

Most Running Toilets Are a DIY Fix, But Not All of Them

Here are a few signs mean it’s time to call a licensed plumber instead:

• Water is leaking from the base onto the floor, not just running inside the tank. This can mean a failed wax ring or cracked component, and continued use risks subfloor damage.
• The tank itself is cracked, or shows a hairline fracture in the porcelain. This isn’t a part swap, and a cracked tank can fail suddenly.
• You’ve replaced the flapper and fill valve and it’s still running. The issue is likely the flush valve seat, tank-to-bowl gasket, or something structural.
• Water is backing up, draining slowly, or gurgling elsewhere in the house when you flush. That points to a drain line or vent stack issue well beyond the tank.
• You smell sewer gas near the toilet, a venting or wax ring seal issue needing immediate professional attention.
• The toilet is a low-flow, dual-flush, or pressure-assisted model with a proprietary mechanism. These often need manufacturer-specific parts, and a mismatched universal part can make the leak worse.
• It still runs intermittently with no clear pattern after checking the flapper, chain, and fill valve. That can mean a hairline tank crack that only leaks under certain pressure conditions.
• You’re not comfortable working near your home’s main shutoff valve, especially in older homes where valves haven’t been touched in years and may seize or leak once turned.

Editor’s Note

You might be wondering about money: how much will it cost me to fix a running toilet? What tools/materials will I need to fix a running toilet myself? How much would/should a plumber cost to fix a running toilet? I know this is what you’re asking because I’d be doing the same. Here’s a table to show approximately how much.

This is what HomeFlash is all about: transparency. We want homeowners to know all their options on the table so they can make educated decisions. Want to do it yourself? Nice, we’re with you every step of the way. Don’t feel comfortable and want to call a pro? No worries, we’ll connect you with the right company. At least now you know approximately how much it should cost.