When by the shop today to check the solar water heater so be sure it was not overheating.
When I got there 1:50 pm the collector was 221°F, the bottom of the tank (heat exchanger) was 192 and the top of tank was 163.

Solar Tank Sensor Reading in Lower Exchanger before the overheatSolar Tank Top Sensor Reading before the overheatSolar Collector Sensor Reading before the overheat


Here is how things were set the first 2 days.
Switch on pump when temperature difference (DT O) between collector and tank lower is 20°F.
Switch off pump when temperature difference (DT F) between collector and tank lower is 13°F.
The tank maximum temperature (SMX) is set on 159°F.
The collector maximum temperature (CMX) is set on 230°F.
The collector emergency temperature (EMOF) turn pump off is set on 280°F.
The collector emergency temperature (EMON) allow pump back on is set on 239°F.
So at T1=221, T2=192, T3=163 the tank was over the maximum temperature and turned the pump off even though the difference was over 20. I the collector gets over 230°F then the pump will activate to try and cool the collector until it drops 6°F to 224°F or if temp. continues to rise and emergency shutdown turns off the pump at 280°F. Also the pump will emergency stop if tank temperature rises above 205°F, so not to boil the tank water.

Leaking Thermal Release Valve

At 3:15 the temperature relief valve on the water tank started releasing hot water. It is set at 203°F.
The sensor at the top of the tank was showing 176°F. There is not a sensor hole in this tank so we had taped and pasted the sensor on the thermal relief valve. I later moved it to the hot water output fitting which was a few inches above the thermal relief valve and may show a hotter temperature.

We replaced the thermal valve form one at Lowes. At that point the roof sensor was showing 280°F!
We ran a lot of hot water out the facet to cool the tank. Next we turn on the system and allowed the pump to run.

The following is what temperatures we recorded February 13, 2011.