Matt Beard wrote:
At a guess I would think that most would cope fine as long as that pipe
used to short the circuit had a radiator in it. I would think that
nasty things could happen if it is just a short bit of pipe - it
wouldn't take much for the boiler firing the heating circuit up to lead
to superheated water ( 100C).

What boiler is it?

Check the instructions. If the boiler already has a automatic bypass,
then it should be ok to isolate the radiator circuit. Otherwise just
install the bypass across flow/return and isolate the circuit below it.