advice needed on draining/ filling a system

[aled]

hi everyone, im a diyer in need of some advice. the job i need doing is to fit a new basin and bath. the system i think is a vented one where i have a header tank and a storage tank with immersion.
on the sysyem i have a rayburn with a drain on it. my question is can i turn rayburn off run the hot water until cold, isolate header tank feed and drain at the lowest point which is on rayburn?

have i got this right or totally wrong end of the stick?

also advice on filling the system please!

 

[jtsplumbing]

Draining from rayburn will only drain small expansion tank, Have a look in your cylinder cupboard, should find a gate valve (Red round handle) that turns off water supply from header tank its also possible that you have another one that turns off cold water to bath room unless cold taps are mains fed, But be carful with old gate valves they can jam shut, if they look old just turn off cold water main and run bath taps until water stops (Storage tank empty) good idea then to replace old gate valves with new full bore leaver valves.