Gas Fitter Practice Test

On a hydronic heater system, what control responds to a load change?

1. Low water cut off

2. Expansion tank

3. Flow switch

4. Aquastat

The correct answer is: Flow switch

In a hydronic heating system, the control that responds to a load change is the flow switch. This device is specifically designed to monitor the flow of water in the system and react when there are changes in the demand for heating. When a load change occurs, such as when a thermostat calls for more heat or when a zone in the heating system opens or closes, the flow switch detects these variations in water flow. The function of the flow switch is crucial for ensuring the heating system operates efficiently and effectively by confirming that the water is circulating properly. If flow is insufficient, it can trigger alarms or shut down the system to prevent damage. Other options, such as the low water cut-off and expansion tank, serve different purposes; for instance, the low water cut-off ensures safe operation by shutting down the system if water levels drop too low, while the expansion tank accommodates the expansion of water as it heats. An aquastat, on the other hand, regulates the temperature within the system but does not directly respond to load changes. Thus, the flow switch is the correct response mechanism in this context.