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The short answer: A running toilet is usually caused by a faulty flapper, a misadjusted fill valve, a tangled chain, or a leaky flush valve. You can often fix it yourself in minutes with basic tools and a replacement part that costs around $10 to $20. If you’re considering a more efficient replacement, check out our best toilet guide for modern, water-saving options.
The flapper is a rubber valve at the bottom of the toilet tank that lifts when you flush and then closes to seal the water. Over time, it warps, cracks, or gets mineral buildup, causing water to leak continuously into the bowl. That leak means the tank never fills completely, so the fill valve keeps running.
How to test: Remove the tank lid, add a few drops of food coloring into the tank, and wait 15 minutes without flushing. If color appears in the bowl, the flapper is leaking.
Fix: Shut off the water supply (valve behind the toilet), flush to empty the tank, and disconnect the old flapper from the chain and overflow tube. Install a new flapper (universal types fit most toilets) by attaching it to the overflow tube and hooking the chain to the flush lever. Use a chain with a little slack (about 1/4 inch) so the flapper seats properly. Then turn the water back on, flush, and check for leaks.
The fill valve (also called a ballcock) controls the water entering the tank. If it’s set too high, the tank overfills and water continuously spills into the overflow tube, causing the fill valve to keep running. If it’s worn out, it may not shut off completely even when the water reaches the correct level.
Check the water level: Look at the water level in the tank. It should be about 1 inch below the top of the overflow tube. If it’s too high, adjust the float: for a conventional float ball, bend the rod downward slightly; for a fluid master style valve, turn the adjustment screw to lower the float.
If the valve is defective: You may hear a hissing or continuous water sound. Replace the entire fill valve (a new one costs about $15 to $25). It’s a simple DIY: shut off water, disconnect supply line, unscrew the old valve from the tank, install the new one, and reconnect. Follow the manufacturer’s instructions for adjustment.
A chain that is too long or tangled can prevent the flapper from closing completely. If the chain is too short, it may hold the flapper open; if it’s too long or looped over the flapper, it can get caught. Both scenarios cause continuous water flow.
Inspect the chain: Look inside the tank and see if the chain has slack. It should have about 1/2 inch of slack when the flapper is closed. If it’s too tight, loosen it by unhooking the chain from the handle and reattaching it to a different hole (most handles have multiple holes). If it’s too long, clip a few links with pliers.
Make sure nothing is in the way: Sometimes the chain or the flapper can get caught on the overflow tube. Gently reposition as needed. Also, ensure the flush handle isn’t stuck in the flushed position. You can spray the handle with silicone lubricant if it feels stiff.
The overflow tube is a vertical pipe in the middle of the tank. If the water level is set above the top of this tube, water continuously drains down into the bowl, causing the fill valve to keep running. This often happens after adjusting the fill valve incorrectly or if the float is stuck.
What to do: First, mark the water level on the overflow tube (it should be about 1 inch below the top). If it’s higher, adjust the fill valve as described in section 2. If the float is stuck, clean it or replace the fill valve.
Also check for a crack: Inspect the overflow tube for cracks or holes. A damaged overflow tube can cause water to leak into the bowl without the flapper opening. In that case, you may need to replace the entire overflow tube assembly (which is usually part of the flush valve). This is a bit more involved, but you can find repair kits at any hardware store.
If you’ve replaced the flapper and adjusted the fill valve, but the toilet still runs, there may be a more serious issue like a cracked tank or a faulty flush valve seal. Sometimes the gasket between the tank and bowl fails, causing a slow leak that makes the toilet run intermittently.
If you’re handy: You can replace the tank-to-bowl gasket (about $10) by removing the tank from the bowl, scraping off the old gasket, and installing the new one. Be careful not to overtighten the bolts.
If you’re not comfortable: Call a plumber. The cost of a repair visit is usually $100 to $200, which might be worth it if you can’t fix it yourself.
Consider upgrading: If your toilet is old, inefficient, and constantly problem-prone, it might be time to replace it. Modern toilets use as little as 1.28 gallons per flush (gpf) compared to older models that use 3.5 gpf or more. This can save you water and money. Our best toilet guide can help you compare top-rated models that are durable, efficient, and easy to maintain.
If the problem persists after replacing the flapper, the issue might be with the fill valve or the flush valve seat. The seat (where the flapper sits) can become rough or corroded, causing a poor seal. You can clean it with a scouring pad, or if it’s severely corroded, you might need to replace the flush valve assembly. Also, check the tank-to-bowl gasket for leaks.
Yes, a running toilet can waste up to 200 gallons of water per day or more, depending on the severity. That can add $20 to $100 to your monthly bill. Fixing it promptly is both environmentally friendly and cost-effective.
It’s generally not recommended. Chemical tablets can corrode rubber parts like the flapper and fill valve, causing them to fail sooner. If you want to keep the tank clean, use a mild vinegar and baking soda solution monthly, and scrub with a brush. If you must use a cleaning product, place the tablet in the bowl, not the tank.
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