A plumber should look at the ______ when a two-piece gravity water closet is continuously running.

• A. Ball cock
• B. Flush valve
• C. Fill valve
• D. Overflow tube

Answer: (B)

When a two-piece gravity water closet keeps running, the path that delivers water to the bowl is the key place to inspect—the flush valve. The flush valve opens to release water from the tank into the bowl and must seal shut after the flush. If the valve or its seal (the flapper) is worn, warped, or not seating properly, it won’t close fully, and water will continue to leak into the bowl, keeping the toilet running.

The fill valve (often called the ballcock) controls refilling the tank after a flush. If it sticks open or the float is misadjusted, the tank can overfill and water can spill into the overflow tube and into the bowl, causing running water as well, but the most direct cause of continuous running in this scenario is a faulty flush valve.