Draining for radiator replacement

Hi,
been here 5 years now....wanting to replace some radiators, but have seen draining can be problematic with BMIII.  Is there a way of removing radiators without full drain? Microborepipes.
I know that top floor could be done by draining top floor.  Is it best to drain from the radiator and not from the BMIII?

Also I didn't realise that the summer warm radiator, that doesn't have a thermo valve, might be a diverter valve.  Is this verifiable other than replacing it and seeing if it works?  Obviously Id use the same drain down to do it.

Header tank self levelled after a shower today.....Hmmm?  Warm, not hot water, in the tank.  No idea what that's about. Otherwise, everything seems fine in water and heating. The tank is right on top of the BMIII unit, so I assumed the warmth is due to that. Just never heard the trickle before.


This forum is excellent by the way. I've fixed many boiler/radiator/tank issues in previous homes but this one looks so scary.  The site just makes it all make sense.

Replies gratefully received.