Aquastats respond to changes in:

Aquastats are devices specifically designed to monitor and control the temperature of water within a heating system. They play a crucial role in maintaining the desired temperature for efficient operation and safety. When the temperature of the water fluctuates, the aquastat responds by either initiating or shutting off the heating process, ensuring that the water stays within a predetermined range.

The focus of an aquastat’s operation is directly related to the water temperature, making option B the correct choice. Understanding this function is essential for gas technicians, as proper temperature control is vital for the effective and safe operation of heating systems, particularly in residential and commercial settings. This functionality highlights the importance of maintaining optimal water temperatures for both energy efficiency and system longevity.

Other options, while related to different types of systems or environmental controls, do not pertain to the specific function of aquastats. For example, air pressure typically relates to gas distribution and combustion efficiency, flow rate concerns the movement of water through pipes rather than its temperature, and humidity levels deal with moisture in the air rather than the physical properties of water within a heating system.