NOCTI Plumbing Practice Test

When a boiler is fed from the home’s water supply, you need to both control the pressure entering the boiler and protect the drinking water supply from any backflow. A pressure reducing valve lowers the incoming water pressure to a safe, stable boiler feed pressure so the system isn’t over-pressurized as water heats and expands. A backflow preventer sits in the supply line to stop boiler water from flowing back into the potable water system, preventing contamination if pressures change or a cross-connection exists. Together, these two components keep the boiler operating safely and shield the plumbing from backflow risks. Other devices like expansion tanks, air vents, or sight gauges are important for system hydraulics and maintenance, but they don’t provide the same combination of pressure control and backflow protection.