Use a hacksaw blade/padsaw to clean out, square up and deepen the slots in the screw heads to give yourself a chance of unscrewing them with a screwdriver. If half the screw head shears off, cut off the other half.
Remove the cistern, then remove the remains of the screws with mole grips afterwards.
Applying a hot soldering iron to the head of a seized screw will sometimes help to free it up, but it's probably not such a good idea if the cistern is plastic.
Remove the cistern, then remove the remains of the screws with mole grips afterwards.
Applying a hot soldering iron to the head of a seized screw will sometimes help to free it up, but it's probably not such a good idea if the cistern is plastic.