The king span solar is the primary heating source for the 80 gallon indirect water heater. Tank is kept at 180 degrees and mixed down. The boiler backs up domestic and does all of the baseboard heat
I have not had a single leak on the pro press fittings. Fittings do cost about 30% more but you will make it up in time.
I have a Triangle Tube Solo 110 boiler with indirect hot water tank. I also have a Thermomax 20-tube solar hot water panel that preheats my domestic hot water in a separate tank. The two hot water tanks are in series. The system has been in place for almost four years with no maintenance required. Eventually, I expect I will need to replace the antifreeze (food grade). The preheat tank is typically heated to about 150 to 160 F most of the summer. Fall and Spring, it will be heated to about 100 F. I live in gray, cloudy Seattle and in the winter, the preheat tank will be about 70 F, which is ambient for the room the tank resides in. Water enters the house at about 48 to 50 F. I am very happy with the system. The one lesson I learned is you MUST have a preheat tank to capture maximum solar btu's. Otherwise, the system would not operate on the many days it could not heat above the domestic hot water preset temp (120 to 130 F).