The convection loop started in reverse again this morning, so I re-plumbed the water side of the system with the hot side going in to the upper element port rather than through the lower element port and the chimney pipe. That didn’t work either. Since I was using shark-bite fittings on the solar loop, I switched the solar hot and cold lines just so see if that would make difference. Nope. I switched them back, cooled down the whole system by refilling it with cool water, and it immediately started pumping in the correct direction and the solar side stayed much cooler than yesterday when the convection loop was flowing in reverse.
We installed 6 sensors on the tank and 4 on the solar loop plumbing around the tank. Tomorrow well install some thermocouples on header and maybe down into some of the evacuated tubes.