Drain down - full or half?

[Serval]

Need to do some work in an upstairs bathroom moving some rad pipes etc.

Just wondering if its okay to do a half drain down, i.e just drain down until all of the upstairs pipe work/rads are empty then top up with water/inhibitor once complete

of is it better to completely drain the entire system then refill as normal?

 

[Ben-gee]

Just drain the top half is fine.