Does a solar water heating system require maintenance?

This is dependent upon the quality of the product as well as the quality of the installation.  Direct flat plate collector systems require little to no maintenance for 20 -30 years.  Evacuated tube systems which were originally designed for the cold European climate in Switzerland, may require you to replace tubes from time to time, depending on climatic conditions and quality of product and installation.  In-direct systems may require you to top up the anti-freeze levels from time to time.  The supplier/manufacturer guidelines should be read and obeyed.  Water quality may also play a part, but essentially, a solar water heating system should require minimal maintenance.