I have a monoblock tap in the kitchen. Recently I lost pressure to the cold tap, only got a slow flow, it started leaking and so did the spout. When the tap was turned on the pressure was fine for a second then turned into a trickle and there was a clunk. I changed the valve unit thinking the internal had come apart and were knackered. The new valve unit is doing the same low flow. the rest of the cold taps in the house are fine, Whats happening???