Some solar cylinders fail due to corrosion. The solar probe pockets are particularly susceptible to this problem. However, we are often successful in sealing them off.
Solar cylinder replacement
If we replace the actual cylinder, we will often recommend to increase the size to avoid overheating and increase solar thermal storage volume.
Newark copper cylinders twin coil solar cylinder with 50-75mm thermal insulation
A new solar cylinder is likely to be better insulated and have a more efficient solar coil than the old one. It therefore can improve the efficiency of the whole solar thermal system.
Alternatives to cylinder replacements
If the main solar coil has perforated, it is sometimes possible to fit a separate heat exchanger. This will allow you to install a solar thermal system whilst keeping your existing cylinder in place.
Willis solasyphon external heat exchanger