The cold tap in the bathroom no longer turns fully.
It was never praticularly tight before but as of yesterday it will only turn about a 180 degrees.
I've not been able to find a great deal of help using Google so I thought I'd post here.
I've tried using some WD-40, but to no avail.
Any ideas what the problem might be and how to go about fixing it.

"The cold tap in the bathroom no longer turns fully."

Before we can help we need more information. What valve is it? Tub? Lavarory? What type? One handle or, as I suppect, two knobs? What brand and how old is it? What do you mean "it doesn't turn fully"? You aren't getting a good flow or the handle's hard to turn? Answer us and we'll get back ASAP. Tom

"The cold tap in the bathroom no longer turns fully."

Before we can help we need more information. What valve is it? Tub? Lavarory? What type? One handle or, as I suppect, two knobs? What brand and how old is it? What do you mean "it doesn't turn fully"? You aren't getting a good flow or the handle's hard to turn? Answer us and we'll get back ASAP. Tom

It is a tub, you suspect correctly two knobs. Both connected to the same (I'm going to call it an outlet bit where the water comes out :). Pushing down on a button makes the water come out the shower head instead. All of this works with the exception of the cold knob.

Normally the you would turn the know through two complete turns to get full flow. The knob only lets you do half a turn now. This is enough to let some water out but not the full flow. The hot knob still works fines.
The brand is shires (which I think is a local, irish, company and may not be much use to you). It's about 10 years old I'd guess.

Oh and pardon my manners,
Thanks very much for the reply

Shut the water ofdf to the valve and remove the cold water stem and washer assembly. (see below) Check the washer and if it's worn or torn replace it. Lubricate the threads with a heavy grease,( we use "plumbers Heat Proof Grease) Next, with the parts still out, turn the water back on to flush out the supply. Reassemble and test. Good luck, Tom

Thanks Tom,
Sorry for the delay in replying but I had to get my hands on a wrench first, before I could remove the cold water stem. However it won't budge.
All I'm doing is damaging the nut, even with insulation tape around the wrench.
The hot stem dissambles with ease for the record.
Is there any plumbers trick I can use to loosen the assembly?

Try squirting some WD40 on the threads and letting it set for a while. Both threads are brass so there's no chance of rust, however, brass will corrode and the WD40 tends to loosen it. For those stubborn nuts I use a large pair of off-set channel loc pliers and as long as I don't damage the threads I don't worry about chewing up the nut. Good luck. Tom