If there is insufficient flow in the hot water system, a probable cause would be the:

The chosen answer highlights a blockage at the screen in the pump section as a probable cause of insufficient flow in a hot water system. In a hot water system, pumps are responsible for circulating water throughout the system, ensuring that it reaches various outlets efficiently. If the screen or strainer at the pump's intake becomes clogged with debris, sediment, or other materials, it can significantly restrict water flow.

When this occurs, the pump struggles to draw in the necessary volume of water, leading to diminished flow rates throughout the system. Identifying and clearing any obstructions in the pump section is essential to restore proper function and flow.

In contrast, while a high pump pressure may seem counterintuitive as a cause of low flow, it generally implies that the pump is operating effectively; if the pressure is excessively high due to obstruction further downstream, that could lead to problems, but it would not directly indicate insufficient flow at the pump itself. Low water levels in the tank can also result in inadequate supply to the pump but would manifest differently than a blockage in the pump. A leaking expansion tank can affect the system's overall efficiency and pressure, but would not typically be the immediate cause of low flow.