Water supply to my washing machine?

I am trying to connect the water supply to a very old washing machine in a house that I have moved into. The plumbing is all in place I think - a copper pipe that runs to the sink's hot water tap splits under the sink to go to the machine. At this junction there is a tap (also copper) and i can feel that the hot water stops at this point. I can move the tap and have tried it in both positions but the water doesn't seem to get past this point. There is also another tap where the copper pipe joins to the plastic one (this tap a plastic switch that swivels between vertical and horizontal) but I don't think the problem lies here as I can't feel the hot water at this part of the copper pipe.

Thanks for any ideas about what I should do.