Cutting out the water supply to your central heating from your boiler will only keep the pressure in your boiler. You will still need to drain your system if you are altering your central heating pipes.

Hi You can not isolate flow and return water in the pipes. to relocate them for a job such as this.
the radiator valves would allow you to isolate the radiator however if you are intending to alter pipe runs then I am afraid you will need to drain down the heating system and bear in mind that upon refilling you will need to add fresh system inhibitor.
personally not knowing your servicing regime I would put some cleaner into in for a couple of days before doing the job as you get 2 jobs for one.
good luck..

Hi,
When boiler is not running then water in heating system (Radiator) is not running either which means no heating but the water stays in radiators all the time to be ready for next time boiler runs. So to change or alter any pipework you have to drain the system (all the water) from radiator and do any any work.
After work complete you can fill the system with filling loop and take air out from radiators.

If it is a combi boiler, you will need to drain the system completely before working on any pipe work. You don't need to turn of any water supply off as it is a combi, you will just drain water from radiators, complete work and then refill system using the filling loop. You tube may have some videos 👍