Worcester Combi boiler drain down

[Pengu]

Hi, can anyone assist me in draining down a Worcester condensing combi boiler as I need to tap into the existing pipework to connect up two resited radiators. I can see from the instruction manual that there is a plastic key which is currently inserted in the slot and there is a small white square plastic tap which has a steel circlip type thing passing through it and its housing.
I'm presuming that turning the key will allow this tap to be turned, or is it that the key itself stops the flow so I can drain off the system and connect up.
Oh and before I forget.....should I replace any inhibitor and if so how.?

Suggestions please....

Many thanks in advance.

Pengu

[Cheesie1]

u need to drain the whole system not just the boiler via a drain cock (usually on rad valve) if ur cutting into the main heating circuit! the white key is part of the filling loop assembly u insert this and turn it to the symbol (open padlock), u then turn the white/grey hexagonal fitting this allows water to enter the system and fill the heating circuit.

[Pengu]

Hi, Just in case I thought I'd better let you know I sussed it.
The key turns the water off, especially if you turn off the boiler. And the square tap at the side of it fills it......simples.

Thanks anyway if you had a look

pengu