How do I use an external filling hose?

The external filling hose (sometimes called a loop) is silver coloured and braided, which is connected between the central heating return pipework and a cold water mains pipe.

It should be located close to the boiler and is often found under the sink if the boiler is in the kitchen.

The braided hose will have a valve fitted on either one or both ends.

Here are a couple of examples of how external filling hoses look:

External filling hose on gas boilers

How to use the external filling loop

1. Make sure both ends are securely attached to the pipes
2. Open one or both of the valves on the braided hose, this allows water to flow into the heating system
3. Watch the pressure gauge rise slowly until it reaches about 1.5 bar (in the middle of the green section)
4. Return valves to original position, this stops the flow of water into the boiler

Watch the video below to see how to use an external filling hose to repressurise a heating system.