What must be ensured for the automatic devices in gas fired heating appliances?

For automatic devices in gas-fired heating appliances, it is crucial that they shut off the flow of gas in the event of a malfunction or unsafe condition. This safety feature ensures that gas does not continue to flow unchecked, reducing the risk of leaks, explosions, or fires. Implementing automatic shut-off mechanisms helps protect both people and property by immediately cutting off the gas supply if a problem is detected, thereby preventing potentially hazardous situations.

The other options pertain to different functionalities that may not necessarily focus on the critical safety aspect of gas appliances. For instance, the notion of manual activation would not align with the purpose of automation designed for safety and efficiency. Additionally, while managing the operation of automatic devices without interference is important, the primary objective remains their role in shutting off the gas flow under unsafe conditions.