In a gas-fired hydronic heating system, water temperature is controlled by a temperature and which sensing element?

• A. Humidity
• B. Flow
• C. Pressure
• D. Density

Answer: (C)

Water temperature in a gas-fired hydronic heating system is controlled using a temperature sensor in the water loop, and it relies on a flow sensing element to complete the control logic. The flow sensing element, typically a flow switch, confirms that water is actually circulating. If there’s heat demand but no flow, turning the boiler on could cause overheating or damage because there’s nowhere for the heated water to go. The combination of temperature sensing and flow sensing ensures the boiler only heats when there is both a temperature demand and a circulating flow, delivering safe and effective operation. Humidity and density aren’t used to control temperature in this loop, and pressure plays more of a safety/pressure-regulation role than a direct temperature control sensing element.