What type of device must an electrically heated heater have to ensure fuel safety?

An approved thermostat is essential for electrically heated heaters to ensure fuel safety because it regulates the temperature within the heating system. By maintaining a preset temperature, the thermostat prevents overheating, which can lead to dangerous conditions such as fuel leakage or combustion. This regulatory function is vital in maintaining the efficiency of the heating system and ensuring that it operates within safe temperature parameters.

The thermostat's ability to control the heating process also aids in energy efficiency, reducing unnecessary fuel consumption and minimizing the risk of equipment failure. Without an approved thermostat, there can be unpredictable temperature fluctuations that could compromise safety, potentially leading to hazardous situations.

While the other options may serve important functions in various contexts, they do not directly fulfill the critical role that a thermostat plays in managing and safeguarding the temperature during the operation of an electrically heated heater.