Kitchen "cold tap" running really slow but all others are ok?

Could be a perished washer shut down water supply and take tap to bits (unscrew from top),if it is a washer replace it,the only other thing I can think of is ,when the new boiler was installed the fitter might have switched of a 15mm isolation valve on the cold water pipe ,you will find this on the cold water pipe under the tap which is not working properly,first check that there is one ,and using a normal screw driver make sure that the screwdriver slot is running parallel with the pipe ,sometimes if they are rushing they don't line it up correctly,good luck