Draining Combi system

[bullethead]

Hi, new here and just wondered if anyone can clarify one or two things for me.
I want to fit a new radiator which means I will 'T' off existing pipework, to do this I will obviously need to drain down the system.
My question is this:
Will the boiler still be able to be used to supply hot water with the CH system drained down? I'm assuming that when the pressure drops due to draining, the boiler won't function?
Any advice gratefully received!

 

[ChrisR]

You're right, it won't work without water in it.
Could add isolating valves where you cut the T in.