Toilet Cistern inlet valve not closing completely

Question

I discovered a wet floor in my granny flay bathroom the other day, and quickly found that the toilet cistern was overflowing. The overflow outlet isn't plumbed to anything, and it's not one of those toilet where the overflow goes down into the bowl. I rent, and getting this sorted out is not by the landlord is sadly not a realistic option.

There's a small button on the inlet. As the float rises the button is gradually depressed, eventually meant to cut off the flow coming into the cistern completely. It doesn't. No matter how tightly I adjust the screw to set the floater maximum height, the inlet still drips. I have to flush the toilet about 3 times a day to prevent overflow. This being in the granny flat means that toilet isn't used daily, so this is a chore.

I'm not clear on the exact terminology here, so here's a labelled picture for clarification

I'm hoping there is a quick easy fix here that I can do myself, without involving my landlord, which is liable to take weeks/months.

Answer 1

Replacing the valve with one that works correctly is the only typical fix for this problem.

The external overflow setup is an annoyance, presumably intentional on the part of the plumbing regulations where you are, .vs. overflowing into the bowl as typical where I am (which leads to a lot of un-noticed toilet leaks that go on for a long time without getting fixed.) If you can get a bucket to catch that it might help if you need to wait for the landlord to get the valve replaced.

If there is an external shutoff before the inlet valve, you could close that. I can't see if there is or not - they are standard where I live.