CH pipework - future proof for ASHP?

[POIDH]

I've a 6 year old Ideal boiler and a bunch of under 10 year old radiators, but on 1970's copper 8mm micro more.
System is losing pressure rapidly, and after boiler service and check I'm pretty sure it's under ground floor. My plan is to replace all pipework and the last old radiator downstairs.
While I'm in there I will also try to insulate the floor as well.
What diameters of pipe to use, assuming that I'm changing the boiler when it dies for ASHP?

[gmaz]

POIDH said:

I've a 6 year old Ideal boiler and a bunch of under 10 year old radiators, but on 1970's copper 8mm micro more.
System is losing pressure rapidly, and after boiler service and check I'm pretty sure it's under ground floor. My plan is to replace all pipework and the last old radiator downstairs.
While I'm in there I will also try to insulate the floor as well.
What diameters of pipe to use, assuming that I'm changing the boiler when it dies for ASHP?

15mm for radiators. The ASHP I'm having fitted will use 28mm to/from the unvented cylinder,

[POIDH]

gmaz said:

POIDH said:

I've a 6 year old Ideal boiler and a bunch of under 10 year old radiators, but on 1970's copper 8mm micro more.
System is losing pressure rapidly, and after boiler service and check I'm pretty sure it's under ground floor. My plan is to replace all pipework and the last old radiator downstairs.
While I'm in there I will also try to insulate the floor as well.
What diameters of pipe to use, assuming that I'm changing the boiler when it dies for ASHP?

15mm for radiators. The ASHP I'm having fitted will use 28mm to/from the unvented cylinder,

Reading online this morning it suggests a larger 'trunk' with 'branches' to the radiators of 15mm. I guess it allows more flow but at lower temperature?