Sorry I am totally confused with what you are saying so I will go through how your boiler works, cold feed is simply that the cold water goes into the plate heat exchanger and comes out of the tap hot, the water inside your radiators and inside the boiler is a sealed system and the pressure is measured by the pressure gauge on the front of the boiler, you top up this pressure and then close the valves and leave , the silver hose must be connected to fill the boiler and can be disconnected afterwards, the boiler has a Pressure relief valve that is set to operate if the pressure exceeds 3 Bar, this vents the water to outside to protect the boiler, you should not have any water coming out of the PRV outlet under normal working conditions