I have been trying to turn off my outside tap for winter. When I turn the valve under the kitchen sink, it fails to stop the outside tap from running. This valve does seem very stiff. I am assuming I have to turn the value clockwise since if I turn it anti-clockwise it actually starts dripping into the cupboard. Anyway, it won't turn off whether I turn it clockwise or anticlockwise. I am assuming some sort of fault with this valve? It is an easy job to fix? Thanks in advance.