Master Plumber Practice Exam 2025 – Complete Prep Guide

An expansion tank serves a crucial role in a plumbing system by accommodating the expansion of water as it heats and subsequently increases in pressure. When water heats up, it expands, which can cause excessive pressure buildup in the plumbing system. An expansion tank provides a space where this expanded water can go, helping to manage pressure fluctuations.

As water is heated—whether in a water heater or through a hydronic heating system—the expansion tank absorbs the additional volume. This prevents potential damage to pipes, fittings, and other components of the plumbing system that could occur due to overpressure conditions. Ultimately, it helps maintain the overall integrity and safety of the plumbing system while also ensuring proper water flow and temperature control.

Other options relate to different concepts: increasing water flow does not directly involve managing thermal expansion, storing excess water is not the primary function of an expansion tank, and while it may have a secondary effect in certain systems, improving heating efficiency is not the main purpose of an expansion tank.