Gas Fitter Test 2026 – 400 Free Practice Questions to Pass the Exam

In a combination heating system, the essential feature for check valves is that they are installed in both the supply and return lines. This is crucial because check valves are designed to allow fluid to flow in only one direction, preventing backflow which can cause inefficiencies and potential damage within the system. By having check valves on both lines, it ensures that the heated water or fluid flows correctly from the supply to its intended location and then returns without experiencing any reverse flow, maintaining the integrity and functionality of the entire heating cycle.

This setup helps in maintaining system pressure and temperature as intended, ensuring that the heating system operates efficiently and effectively. Having check valves only in the return line or only in specific orientations would not provide the comprehensive backflow prevention needed in a combination heating system, and thus would not support optimal performance and reliability. The pressure rating, while important in ensuring the valves can handle the system's operational pressures, is not as fundamentally critical as the proper installation of the valves in both the supply and return lines.