A test is performed at a pressure of 5 bar before flooring, screed or biscuit mix is laid to check for leaks and ensure the pipes are at their most expanded. This pressure is to be maintained until screed application is completed in order to ensure that any leaks are identified immediately and prevent the screed cracking later. 6 bar is a lot higher than a system would normally run.This action can be pressurised for testing purposes with mains water in most cases. REMEMBER: You must be extremely careful to avoid frost unless anti freeze has been added to the water. The flow from the mains tap to the filling point on the flow rail (red) of the manifold and the return/waste hose connected from the drain point of the return manifold (blue) to somewhere the return water can drain to.