A central heating filling loop is used to re-fill (re pressurize) a central heating system with water.
It is not part of the boiler but will connect, and therefore be close, to the boiler.
The filling loop allows the user to manually increase the volume of water within the central heating system if the pressure has dropped too low. Filling loops can be internal or external, depending on the type of appliance you have. If the filling loop is external to the appliance it is usually removable due to water regulations. However, if the loop is internal, there is usually a key that can be removed to disconnect the filling loop after use.
