I would advise not using these kits by novices, who tend to work
slowly and may come to a sudden stop when they discover the bit they
have forgotten. It is not good to then be worrying about the ice
plugs melting.

You strike a chord there as I often find the necessity to visit the diy shed
in the middle of a job.

I suggest draining down the whole system, as had been said this is
the time to fit drain points to make future work easier. If
necessary you can then put in a system cleanser (if you don't know
the history of the system), then inhibitor. These can be put into
radiators with a suitable gadget, there should be instructions with
the bottle it comes in.

The boiler is in the garage and the rad to be worked on is in the upstairs
bathroom. I will probably be able to just drain that one down without
needing to drain the whole system as it is quite recent, no more than two
years old.

Roger R