The pressure is on 0 – where is the filling loop?
• The filling loop on sealed systems of the past was connected into the system pipework between the cold water mains and the heating return. Regularly it was quite difficult to access it as it was hidden in the back of a kitchen cupboard or below the work surface. Many appliances are now fitted with an internal filling loop. This is located underneath the boiler itself. If your boiler doesn’t have an internal filling loop, then one must be fitted externally between the mains water and the heating circuit. This can be on rigid pipework but predominantly is identified by a flexible pipe. Conventional boilers do not usually require a filling loop as the feed and expansion tank in the roof space tops up the system as required.
