What is the reason solar mate is leaking? Me and few neighbor is having a leaking water heater from the valve.

I have ask a contractor to change the valve,  but he didn't change it and said the whole think need to be change, and charge me 180 for the visit.

What can I do, neighbor water is flowing to my house gutter and cause it to rust and leaking, some other neighbors water is flowing to the backyard house.

This Solar mate is causing a mess.