How can I fix my Simpson esprit 700 washing macine?

When i put a load on the cold water just trickles out. the hot comes out nice and fast but the cold is very slow. It takes hours to fill the machine. I have checked the hose and it is fine as when disconected from the machine the water comes out fast. But when I connect it to the backof the machine it just trickes through when we put it on a wash cyscle.