Central heating pipes and rads

[G1zm0]

Im wanting to upgrade my central heating before I get a new boiler fitted .

What I have just now is 2 rows of 15mm copper pipe running under floor with no installation. (Flow and return)

From each piece it feeds 4 radiators from 1985 with microbore pipe , think its 8mm.

The boiler is having trouble pushing heat I presume as it comes on for a minute then turns on for a minute ( it heats 1 degree every hour)

Under floor I have a crawl space about 1.5 foot that I can get under . And 2 foundation walls that the microbore goes over to the rad.

I was thinking of replacing the flow and return with 22m, and using 15mm hep pipe to connect the rads .

The floor is laminate and tile, would (one part i can go down is under carpet.)
Would I be able to connect the 15mm pipes to the microbore pipe and pull them through from the top to the new pipe .

 

[muggles]

Depends how much free space there is, but bear in mind a 15mm fitting is about 25mm in diameter. Might be easier with 10mm? You'll need to do a special order for 8mm push fit online if that's what you want to use to pull it through though, as it's not available at most merchants