i think i have a feed and return system . the rads are not getting hot down stairs if the rads are hot up stairs when we moved in to the house there was no caps on the rads so not no which is the in and out. i have tryed bleeding them but no air comes out just water if i bleed them for a while hot water comes through but rads don't get hot in the mornings there is a knocking and creaking noise coming from loft can somebody help please