do you change hot pipe size when changing to a combi boiler

[pmchammer]

can anyone tell me if you need to make the hot supply to outlets half inch when changing to a combi boiler

[plumbbob]

It would not be usual to down size the pipe simply because of fitting a combi boiler. If you are changing pipework, use 15mm instead of 22mm.

[htg engineer]

It is best to, as the supply to the boiler is 15mm, having a 15mm draw off, reduces the heat loss. As you cannot get more water out than you put in, there'll always be cooler water in the 22mm pipework.

htg