Primary circuit unvented cylinder

[pencil]

How do I drain off and refill the primary circuit of an unvented cylinder with the intention of removing a rad and replacing it with a heated towel rail. Perhaps a drain down is not necessary.

 

[g20]

Do you mean how do you drain down the individual radiator and replace it with a towel rail, without having to drain down the whole heating system?

you cant!

 

[pencil]

If you read the question again, I ask 'how do I drain down the primary circuit?'