1. Worn Out Flapper Valve
The rubber flapper at the bottom of the tank degrades over time. If it does not seal properly, water continuously leaks into the bowl.
2. Incorrect Float Height
If the float ball or cup is set too high, the fill valve never shuts off, causing water to constantly drain into the overflow tube.
3. Faulty Fill Valve
If adjusting the float does not work, the internal mechanisms of the fill valve might be broken, requiring a complete replacement by a plumber.