Before testing a low water fuel cut-out, what must be done first?

The correct answer highlights an important safety procedure in the operation and maintenance of boilers. Before testing a low water fuel cut-out, it is essential for the burner to be on. This step is crucial because the low water fuel cut-out is a safety device designed to automatically shut off the burner if the water level in the boiler drops below a certain point. By having the burner on during the testing process, the operator can verify that the cut-out functions correctly by observing whether the burner shuts down appropriately in response to the simulated low water condition.

In this context, ensuring the burner is operational allows for an accurate assessment of the safety mechanism. Testing the cut-out while the burner is off would not provide useful information about its performance, as there would be no running condition to observe the response. It's vital to follow established procedures for testing safety devices to ensure boiler operation remains safe and compliant with regulations.