How can the high limit control be tested?

The high limit control is a safety mechanism designed to prevent dangerous overheating of a boiler or other heating systems. Testing this control typically involves manipulating conditions to see if it functions correctly.

Raising the boiler pressure above the operating setpoint will effectively test the high limit control because it simulates a situation where the system may exceed safe operating conditions. If the high limit control is functioning properly, it should activate and shut down the system once the pressure exceeds the predetermined limit, thereby confirming that the high limit control is operational.

The other methods, such as reducing the temperature or adding more water, may not effectively test the control's capability to respond to high limits or fail-safe conditions. Checking the power supply is important for ensuring the control device is operational, but it does not confirm that the high limit control will react correctly under emergency conditions. Thus, focusing on the pressure check is the most effective way to verify the high limit control's functionality.