How can I fix my Simpson esprit 450 washing machine ? The cold water valve?

How can I fix my Simpson esprit 450 washing machine ? The cold water valve may need replacing as only a trickle of cold water runs through. I have taken off the hoses & the cold water is strong thru them but once connected to the machine there is not much cold water coming thru . Also how much would this cost a repairman to do this ?