Fixing a drip from Vaillant unvented hot water cylinder cold inlet

Hi All

Would a fix for this be something an amateur DIYer could do?

Drip drip drip from the cold water inlet 'overflow' - where the cup is hanging in the picture (see red arrow, bottom half of pic). The cup 250cc fills up about once a week at the moment.


Happy to provide better pictures if helpful.

If DIY-able, what part am I looking for / how can I tell?

Many thanks in advance for help and advice!

 

It's a sealed system, personally ide either isolate if you can else drain it down.
If you get another exact valve you may be able to replace the rubber seal inside the valve, that is what I did with mine.

 

Try tightening the square end on the right hand side, it may just need nipped up.

 

Hi
Just to let you know that I tightened that square end. Was very hard to turn - even just a tiny bit.
That seems to have done the trick - been 10 days and not a drip
Many thanks!