Hot tap will only open slowly

[IKnowNothingAboutDIY]

Apologies if this is a very stupid question but having trouble with one tap in our kitchen.
Basically it will only open if you turn it very very slowly and will eventually open and work fine.
It seems to work slightly better once opened and can be opened/closed slightly more quickly for a while but soon reverts back to the need to open it super slow.
If not opening slowly it just "locks up" and need to turn it back a bit the other way and then open very slowly again.
It's only the hot tap in the kitchen that does this and sounds like its making almost a juddering sound upstairs when it's struggling to open.
Being a total amateur I'm not sure if this is a likely problem with the tap, or pipes, some kind of washer/valve, or air. The hot taps upstairs work fine.
Any ideas what the likely cause (or causes) are as I'm not sure where to start?
Many thanks in advance for any help/advice anyone can give.

 

[polesapart]

Quarter turn lever or traditional tap head, and do you have a hot water cylinder?

 

[polesapart]

Either way the solution is probably to replace the tap spindle/cartridge.

 

[IKnowNothingAboutDIY]

Quarter turn lever or traditional tap head, and do you have a hot water cylinder?

Traditional tap and no cylinder. Just a Worcester Bosch Combi close to it.

 

[JohnD]

Take it apart and replace the washer. While you have it apart you may find a horseshoe clip on the spindle, that might have come out of place, and a thing that screws in and out with a left-handed thread. Either of these may have come out of place, or be scaled up, or worn. If the washer is badly worn, the thing may be screwing down too far and coming off its thread. Clean up the parts with a green nylon pan-scourer, and preferably lube the moving parts with white silicone (plumbers) grease.

When you reassemble it tighten up the gland nut on the top.

I don't actually know which part will be worn or dislodged, but a traditional tap is pretty simple, I bet you'll spot it when you have it apart.

If need be you can fit a new cartridge. Count the number of splines on the spindle before you buy a new one, and measure it carefully. There is a huge variety, especially if it is some unknown import. A UK tap maker will probably have online parts ordering. Your DIY shed will stock one or two. Specialist suppliers sell hundreds. http://www.shop.lunns.net/tap-spares-8-c.asp

 

[IKnowNothingAboutDIY]

Thanks chaps. Will investigate further.

 

[IKnowNothingAboutDIY]

Just coming back to say thanks again. After a bit "fun" trying to coax an ancient stopcock into moving, I moved on to opening the tap and it was indeed a knackered washer, that was almost in two pieces. Replacement in and everything's working nicely again now.