My Solar Thermal system was built of high quality materials and could have potentially lasted many more years if it had not suffered from the ‘Achilles heal’ of using glycol transfer fluid which caused frost damage by cracking the manifold.
Despite the good quality of the product and installation, the system was not a success from the outset because of the most common problem with thermal solar installations - it overheated during sunny periods as there is no way to disconnect the heat source from the solar circuit once it had received all the solar power input that it needs, or can cope with. This resulted in the glycol solution being released as steam through the pressure release valve on the roof above the manifold. Glycol systems need to be regular cleaned / flushed out if fouling is to be avoided which can damage the solar circuit and pump through clogging with semi solids etc.
https://robertkyriakides.wordpress.com/2009/08/20/anti-freeze-agents-in-solar-systems/
Consequently the solar circuit had to be regularly refilled with glycol solution due to overheating when the weather was fine and covered with tarpaulins when we went away from home. I now know that glycol solution needs to be replaced if has been overheated else it fails to protect systems against freezing and causes destructive corrosion. Glycol systems need to be regular cleaned / flushed out - if you can find that rare commodity - a competent regular service provider.