Toilet Won't Stop Running — How to Fix It in Minutes

A running toilet wastes up to 200 gallons of water a day and can add $50 or more to your monthly water bill depending on local rates. The good news: this is almost always a cheap, simple fix. The three most common causes each cost under $15 in parts and take less than 10 minutes to replace.

What's Happening

A toilet that runs constantly — or cycles on and off by itself — means water is leaking from the tank into the bowl when it shouldn't be. There are three parts that cause this, and figuring out which one is the problem takes about 30 seconds.

The flapper is a rubber seal at the bottom of the tank. It lifts when you flush and drops back down to seal the tank. If it's warped, cracked, or gunked up with mineral deposits, water slowly leaks past it into the bowl. This is the cause about 80% of the time.

The fill valve controls the water coming into the tank after a flush. If it's failing, the tank overfills and water drains continuously through the overflow tube.

The float tells the fill valve when to stop. If the float is set too high or is stuck, the tank overfills and water runs into the overflow tube nonstop.

What to Check

1. Remove the tank lid and look inside. Set the lid somewhere safe — porcelain is heavy and cracks easily. You'll see the flapper at the bottom, the fill valve on the left side, and the overflow tube in the center.
2. Check if water is going into the overflow tube. If water is streaming over the top of the overflow tube, your float is set too high or your fill valve is faulty. Adjust the float first (there's usually a screw or clip on the fill valve — turn it to lower the water level about 1 inch below the top of the overflow tube).
3. Do the food coloring test. If water isn't going into the overflow tube, put a few drops of food coloring into the tank water. Wait 10 minutes without flushing. If colored water appears in the bowl, your flapper is leaking.
4. Inspect the flapper. Reach in and touch it. If it feels rough, stiff, warped, or slimy, it needs to be replaced. This is a $3-8 part at any hardware store — just bring the old one with you to match the size.
5. Check the flapper chain. If the flapper looks fine, check that the chain connecting it to the flush handle isn't too short (holds the flapper open) or tangled (keeps it from seating properly). There should be about half an inch of slack.

When to Call a Pro

A running toilet is one of the safest DIY repairs you can do — no electricity, no gas, no structural risk. That said, there are a couple of situations where a plumber makes sense:

What This Typically Costs

A flapper costs $3-8. A universal fill valve kit costs $8-15 and includes the float. Both are available at any hardware store and install without tools. A plumber will charge $150-300 for the same fix because of the service call minimum, even though the part and labor take under 15 minutes.