A toilet that runs constantly is usually caused by a worn flapper (the rubber seal at the bottom of the tank), a misadjusted float, or a failing fill valve. The most common fix is replacing the flapper — an inexpensive, homeowner-friendly part. Open the tank and watch what happens after a flush: if water keeps trickling into the bowl, the flapper likely is not sealing. If adjusting or replacing these parts does not stop it, a plumber can diagnose a deeper issue.
A running toilet is more than an annoyance — it can waste a surprising amount of water (and money) over time. The good news is the cause is usually one of a few simple, cheap parts inside the tank, and diagnosing it just means lifting the lid and watching.
The most common culprit is the flapper, the rubber seal that lifts when you flush and is supposed to drop back to seal the tank. Over time it warps or wears, letting water leak continuously into the bowl, which makes the tank refill over and over. Replacing a flapper is inexpensive and one of the most DIY-friendly plumbing fixes there is.
If the flapper looks fine, check the float and fill valve. A float set too high lets water rise until it spills into the overflow tube, running constantly; adjusting it down can fix that. A worn fill valve that does not shut off properly is another common cause and is also a replaceable part.
If you have swapped the flapper, adjusted the float, and the toilet still runs — or if the problem is a leak at the base rather than inside the tank — it is worth calling a plumber. Persistent issues can point to a cracked component or a problem beyond the simple tank parts.
Looking for a plumber in NYC?
Find a plumber in NYCFrequently Asked Questions
Why does my toilet keep running?
Usually a worn flapper that isn't sealing, a float set too high, or a failing fill valve. Lifting the tank lid and watching after a flush usually reveals which.
Is a running toilet easy to fix myself?
Often yes — replacing the flapper or adjusting the float are inexpensive, DIY-friendly fixes. If those don't stop it, a plumber can diagnose a deeper issue.
Does a running toilet waste much water?
Yes, it can waste a significant amount over time, which shows up on your water bill — so it's worth fixing promptly even though it isn't an emergency.