Does this valve need replaced or just tightened?

[andrew.lees84]

I have a leaky radiator valve in my house. I've tried just tightening up the nut, but I'm really struggling to move it. Just wondering if tightening is all that's needed or did this valve need replaced? Hopefully it's clear from the photos that there is a lot of black oxidisation on the valve and I wonder if that's perhaps preventing a tight fit now?

 

[Geofd]

I would just replace it it has a union on each side so as long as you drain the system down you should be ok