Kitchen tap no hot water.... Isolation valve the culprit?

[Bowness72]

Hi.... I've got a problem with my kitchen tap and think it's the isolation valve causing the problem but just thought I'd ask for a professional opinion before draining and replacing.
When I turn the hot tap on I get a trickle of water. If I turn the cold water tap on it runs fine. Old style mixer tap with valves not cartridges... See photo.
First thing I did was check upstairs taps both hot and cold taps working fine. Then I looked under sink to check whether isolation valves were installed as I planned to replace tap,

but then I noticed the isolation valve had a coating of white substance (see photo) and when I turned screw a tiny drip of water leaked out of the screw thread.
Does it sound to you guys like it's the valve corroded/blocked that's preventing hot water getting to the tap?

Thanks for any advice

 

[terryplumb]

No its the tap valve

 

[Madrab]

Undo the hot tap 3/4 open and then pull up on the tap, it should let some water out. If so, aAs @terryplumb mentions, it's the tap washer. You can replace that itself or buy a set of tap revivers, or a whole new tap even.

 

[Bowness72]

Thanks guys.... I've had the tap stem off already, but didn't really tell me anything. The tap is quite old and green/corroded anyway so think I'll replace it and the isolation valve too as that's leaking quite a bit now too.
Cheers