My double flush toilet has developed a fault. It won't stop filling eve when I pull the float arm right up. I have replaced the inlet valve diaphragm

[ShaunCorbs]

Yep less chance of cross threading when it comes to the bottom nut

 

[Chriswareham]

My double flush toilet has developed a fault. It won't stop filling eve when I pull the float arm right up. I have replaced the inlet valve diaphragm but this has made no difference
What else can i try?

Replace the valve as the diaphragm has not been fitted properly.
There must be water coming from the pin so that it builds up pressure on the - side of the valve so that it shuts off