Answer:
If a toilet is cycling on and off and the tank is refilling every few minutes, the first thing that should be checked is the flapper. The flapper is a rubber valve that covers the opening at the bottom of the toilet tank and allows water to flow into the toilet bowl when the toilet is flushed. If the flapper is not sealing properly, water can leak from the tank into the bowl, causing the toilet to continuously cycle on and off. Checking and adjusting the flapper is usually the easiest and quickest solution to this problem. Other potential causes of a toilet cycling on and off, such as a faulty fill valve or a clogged overflow tube, can also be checked if the flapper does not fix the issue.