Why is my toilet running constantly?
Common Causes
The most common culprit is a worn or misaligned flapper—the rubber valve at the bottom of the tank. If it doesn't seal properly, water leaks into the bowl, triggering the fill valve to run. Another cause is a faulty fill valve (ballcock) that doesn't shut off when the tank is full. The float might be set too high, causing water to spill into the overflow tube. Less commonly, the flush valve seat or the refill tube could be the problem.
- Worn flapper that doesn't seal
- Fill valve not shutting off
- Float set too high
- Flush valve seat damaged
- Refill tube mispositioned
How to Diagnose and Fix
First, turn off the water supply and flush to empty the tank. Inspect the flapper for cracks, warping, or mineral buildup. If it's not sealing, replace it (a new flapper costs a few dollars). If the flapper looks fine, check the fill valve: adjust the float so the water level is about an inch below the overflow tube. If the valve still runs, replace it. For a leaky flush valve seat, you may need to replace the entire flush valve assembly. Many toilet repair kits include both flapper and fill valve for under $20.
When to Call a Plumber
If you've replaced the flapper and fill valve and the toilet still runs, the issue might be a cracked overflow tube or a problem with the water supply line. A plumber can diagnose and fix these. Also, if you're uncomfortable working with plumbing, it's worth calling a pro—it's usually a quick, affordable repair.
Common mistakes
- Ignoring the problem—it can waste hundreds of gallons of water per day.
- Replacing the fill valve when only the flapper is faulty.
- Not turning off the water supply before making repairs.
