glo-worm spacesaver 45-60b?

Hi , I have seen your reply re a post on a similar problem with my boiler , the boiler has started to make a noise when the central heating is on and a couple of the radiators are noisy , I bled them this morning till the water ran free , I believe I need to open a valve somewhere to top the water up can you advise where I might be able to locate this . there are some boxed in area’s around the boiler, following the pipes attached to it . I have taken a couple of the ones I can access off but cannot locate a valve , any help or suggestions would be very much appreciated , also would you be able to advise where I might find a manual for the boiler online ..