Christian

On the Boiler itself there will be Flow and Returns, both marked up.

BUT if you are using Thermostatic Radiator Valves, they are bi-directional, so you can fit it to which side of the radiator you want. Just double check that the Valves you are fitting are first.

Depending on what boiler size you have, the DHW MAY be 22mm, but it will say in the instruction Booklet mate.