I have just replaced a radiator and about 6m of pipework in a room we are remodelling. Works fine.
The radiator instructions state that the system should be flushed with a cleaning product then a protection product added (inhibitor, I assume) after being fitted.
We have only moved in to this house recently and it has a Potterton Kingfisher CF 40 (or 50 or 60) boiler - pretty old. There is no expansion tank in the loft (just cold water storage) and there is a copper cylinder in the upstairs airing cupboard. I cannot see a fill loop and the water pipework appears to be behind the boiler which is completely inaccessible. I can't see a pressure gauge either.
So I can't see any way to drain or fill the system, and the manual is not helpful.
How should I proceed?