Which of the following is NOT a possible cause for machine overfilling using a liquid level control?

In this scenario, the focus is on identifying a cause for machine overfilling that does not relate to the operation of liquid level controls. A faulty control indeed can lead to improper functioning, but it does not inherently cause overfilling when it is not functioning properly. Instead, it may manifest in ways that affect how the control responds to liquid levels.

On the other hand, issues like scale build-up can impede the operation of level sensors, leading to false readings and potential overfilling. Similarly, a broken wire could disrupt the signal between the sensor and the control system, resulting in an erroneous condition where the machine continues to fill despite reaching an adequate level. Likewise, a bad ground can create issues with the electrical flow or signal integrity, which similarly might lead to overfilling by not properly communicating the liquid level.

These issues are more directly linked to the mechanics and the electrical functioning of the machine itself and could reasonably lead to overfilling scenarios. Therefore, identifying faulty control as not being a direct cause for machine overfilling highlights the distinction between internal defects that influence sensor operation versus conditions affecting the machine's electrical system.