these modern replacements to the ballcocks can have life of their own, mine broken because I have a big flush and small flush button on top of mine and when pushed the one pressed in can get stuck under the adjacent button, which resulted in the toilet flushing constantly however it was not big time flushing it had effected the float system and was just refilling the cistern constantly which through the over flow system emptied into the bowl.
I had to turn the water to the toilet off but for some reason weeks later when I had used the toilet and forgot to turn water off again it appeared to be fixed anyway and not overflowing, was just about to pay to get it fixed.
It still fills slow though...... so
'Builder' is there any way to change the flow volume 'in' to make it fill quicker or is it fixed or based on the pressure in the water pipes?