When a toilet flush valve or flush amateur runs continuously, what is the most common problem?

When a toilet flush valve or flush mechanism runs continuously, a common issue is that the orifice in the diaphragm is plugged. The diaphragm is a crucial component in regulating water flow during the flushing process. If the orifice becomes blocked, it can prevent the diaphragm from functioning properly, causing the toilet to continuously run as it tries to manage water flow.

In this scenario, the excess water running is essentially an attempt to flush; however, since the passage is obstructed, the system cannot create the necessary seal or flow regulations needed for stopping the water. Flushing mechanisms rely on pressure and proper function of these parts to work efficiently, and a plugged orifice disrupts that balance.

While other factors might affect toilet performance—such as too long a chain causing the flapper not to seat properly or issues with the flapper not being tightly sealed—these do not represent as direct or common a failure as a plugged orifice in the diaphragm. In contrast, a shut-off water supply would not lead to continuous running, as there wouldn't be any water flow at all. Thus, the plugged orifice is indeed the most frequently encountered problem leading to this issue.