About boiler operation and control, rules and regulations may vary due to national application. Nevertheless, it is clearly stated in the regulations that when there is a high safety issue, the boiler should operate safely without human assistance.
Running a boiler without water can be very dangerous. Due to the high pressure inside the boiler, the water vapor expands and exerts a force on the boiler wall. An explosion may occur when design limits are exceeded. If the water level drops to a preset low water level, the level controller will immediately shut down and lock the boiler's burner. Manual reset is required even if the burner is fixed.
To prevent such extreme hazards and safely lock the boiler burner, the low alarm limiter should be used. The limiter is used to monitor the minimum fill level of water in the steam boiler. If the water level is below the minimum water level, the limiter should turn off the burner to prevent overheating before personal injury or installation damage. The horizontal controller self-tests 52 times per second. Therefore there is no need to test the controller button.