What safety device is typically fitted to unvented hot water systems?

An expansion relief valve is an essential safety device fitted to unvented hot water systems to manage excess pressure caused by thermal expansion of the water. In an unvented system, water is heated in a contained space without the need for a vent to the atmosphere. As the water heats up, it expands, and this increase in pressure needs to be safely managed to prevent potential hazards such as bursting of the tank or piping.

The expansion relief valve is designed to open automatically when the pressure reaches a predetermined limit, allowing excess water to escape and maintain a safe operating pressure within the system. This function is critical for preventing damage and ensuring the system operates safely.

In contrast, while devices like thermostats, pressure gauges, and flow control valves play important roles in water heating systems, they do not specifically address the issue of thermal expansion and pressure management in the same way that an expansion relief valve does. Thus, the presence of the expansion relief valve is crucial for the safe operation of unvented hot water systems.