Stick with 10mm, or can I use 15mm?

[Sponge]

I need to change and move the position of a bedroom radiator. It's going from an internal wall, around the corner, to an external bay. It'll probably require no more than 8m of pipework.

The system is 10mm microbore, which I would have to buy if I'm going to keep the same.

However, I have 15mm available and wondered if it would adversely effect the performance of the system if I used that instead.

 

[dcawkwell]

Go to 15mm. Since the 15mm will be connected to the existing 10mm won't make any difference.
At worst a little balance of the system afterwards.