what do I need to replace in a leaking Bellavista toilet cistern?

Toilet cisterns used to overflow to outside the property - but the modern arrangement is to have them overflow into the toilet bowl.

Your cistern is overfilling and overflowing - it needs the inlet valve to be adjusted to shut off sooner - there's usually a float arrangement that bears on the inlet valve - lower the float to have the valve shut off sooner.

There is usually a maximum fill mark on the inside of the cistern.

There is often a locking nut on the adjustment screw.

Operate the flush several times to see what's going on - pull up on the float arm to watch the valve shut off.

Good Luck...
September 2015