JG Underfloor Manifold Isolation Valve is a replacement valve for that thermostatically opens the return port for the associated manifold circuit when in use and closes when shutting down. Installed on the return bar of the manifold, the valve opens as hot water is pumped through the circuit slowly opening as the temperature rises. The valve closes automatically as the system shuts off and cools. Durable brass Suitable for JG Underfloor heating manifolds manufactured prior to April 2014