What does quartz sleeve mean in practice?
The sleeve keeps the electrical UV lamp dry and must transmit UV-C without deposits of scale, iron or grease.
When does it matter?
Even a thin coating can significantly reduce the delivered UV dose, while a microcrack can allow water into electrical components.
Which solutions are related to it?
Clean the sleeve with a quartz-compatible agent, inspect it against the light and reinstall it with new or serviceable O-rings.