you have to use the filling loop to add pressure to the system take care not to over fill the system the tap to add pressure looks normaly like a tap used on your washing machine a may be short of the handle if so remove one from your washing machine pipe or dish washer you will need a small screw driver for this fix it to your loop valve and add pressure to about 1.5 bar this can be done with a small spanner but you are better to use the handle as you can tell when you have turned the water back off remember when you bleed a rad you need to add water to bring your pressure back up to 1.5 bar (aprox)