I want to drain my central heating so that I replace a faulty mid-position
motorised valve.

Now I have found two drain cocks in the system.

i) On the bottom of a downstairs radiator - lowest point in the system
ii) On the return pipe to boiler. This is about 6.5 feet so is above
downstairs radiators

Now I have questions about them both.

The low drain cock (i) has a square drive the same dimensions as a radiator
vent. However, it is in a recess which is circular but with one flat edge.
This means you can't get a vent key into it. At first I thought the flat
was where it had been bashed by the installers but on closer inspection it
has been manufactured like that. Is there a special tool to operate this?

The high drain cock (ii) can be opearated easily but I don't see how this
will drain the system. Is this because it is only meant to drain the
upstairs or are you meant to have the pump on so that the water is pumped
out. If you are meant to use the pump, how do you get it to operate without
the boiler on.

Thanks for any advice.

Cheers,

Nigel