hi, could be the tap is a non rising head type of tap, i would turn off the hot water supply ensure you have done so by opening another hot tap in house , then remove tap top and using adjustable spanners undo tap valve body , you may find that the lower partof valve has worked it self loose and the threaded body will need threading back together , its quite often a problem on this type of tap, just put it back together and it should be ok
plumbermanalan
August 2008