I'm upgrading the plumbing prior to having a Combi installed. I'm going to
put in a number of (full bore) isolation valves on both the DHW and heating
circuits in order to make it easier to do additions/changes later, without
having to drain down the whole system.

How near the boiler can the valves be? I know the last metre or so of
pipework to the boiler should be in copper (not plastic); since the valves
have a rubber (neoprene?) seal, is there a recommended minimum distance from
the boiler to a valve?

Also, if the engineer wants to make a soldered joint, is there a minimum
distance between the joint and the valve, to avoid heat damage to the valve
during soldering?

Cheers