Half turn on tap before water comes out

[u0362565]

Hi all,

On one of our cold taps i have to turn the handle about a half turn before the water starts to come out. I have taken the handle off to reveal the valve assembly and notice that on the top section where the head with splines is, this can be turned some way in either direction when the tap is off (i.e. valve closed), there is some play in the splined head. The head which has the splines seems to be on a thread into the rest of the valve. When the head is tight closed clockwise and i start to unwind, the splined head starts to unscrew from the rest of the valve on its thread then after about a half turn friction is felt and then the water comes out-The valve is engaged and is lifted. The remedy would seem to be to stop the splined head from turning relative to the rest of the valve but as its on a thread its as if it should turn. The hot tap seems to be a slightly different valve design as there is no way for the splined head to turn on its own relative to the rest. Hopefully my explanation makes sense, not sure what all the valve parts are called.

Thanks for the help!

 

[JCplumb]

Not sure if I'm reading this right.
Are you saying that the splined 'nipple' that is the top part of the valve turns some way without turning the actual valve?
I'm presuming you have 1/4 turn ceramic valves.
If that's the case then the top ceramic disk has worn and you need a new valve.
Common types are readily available at plumbers merchants. Also from places like B&Q or Screwfix, but you will be guessing because they're blister packed and there are lots of different sizes.
Take your valve out and get to an independant merchants for a replacement.
It's good practice to change them both at the same time because the other valve is likely to be as old and worn as this one.