Hi i'm looking at adding 3 radiators to my heating system, the boiler
is a combi and only 18months old. It can take 14 radiators. I will
check the max btu it can take, and make sure it's all ok. I only have 6
radiators on the house at the moment.

Now i have looked in the kitchen attic and the boiler has 2 22mm pipes
coming out (F&R) and they then go into a 15mm (F&R) pipes ones goes
left the other right, now the one going rights feeds 2 radiators the
kitchen and bathroom. And the other on feeds the whole of the house,
bed1, bed2 then comes downstairs and feeds the living room and dining
room.

Now i'm looking at adding 2 upstairs in Bed 1 and landing and one
downstairs the hall (this will come from upstairs.

Now i know you should really only have 3/4 radiators off 1 15mm run so
i'm maxed out coming off the run that's there.

How do i go about making a new return and flow so can feed the new 3
radiators i require?

I've done a little reading, is it just cutting into the 22mm with a
15mm 't' joint and then feed that up and then feed each radiator, and
doing the same with the return?

I know i need to drain the system aswell.

Any help would be great