Pumping to collectors at night, lowering tank temperature

Anthony Rice in Louisiana installed an 80 gallon "E" (electric element) drainback system with a single Aurora 4' by 10'. No shade issues, good solar orientation. The system was installed on Saturday, January 15, 2011. Sunday was cloudy. Monday was full sun.

The SHEM 32"E" controller was programmed by the homeowner to the following settings:

Tank temp at 135-140 degrees, between 0 and 23:59. This time setting is correct, as it is military time, does not exceed 24 hours, and has no overlaps.

On Monday afternoon at 2:30, the tank reached 149 degrees, as the pump circulated solar heated fluid through the solar loop. However, the pump continued to pump until past 3:30 as the sun set and the collectors cooled. The pump continued to circulate fluid until the tank temperature was reduced to 140 degrees, when the pump shut off.

The question is: how to set the controller so the pump will not circulate fluid and cool the tank?

Maurice with Sun Energy also called with this issue. To resolve the issue, we checked controller settings. It appeared that the CMN (Collector low temperature protection) had been turned on.

Returning the controller to factory settings did the trick for this repair.

CMN (Collector Low Temperature Protection) is set at 50F. At this setting, the collector loop will not activate unless collectors are at least 50 F.

CFR is a frost protection feature for Glycol installations. This should be deactivated for drainback installations.

To return to factory settings, use the LOAD setting. Holding down "SET" for three seconds will produce three buzz tones. This indicates factory settings are restored.

We have tested the reset feature by resetting various features, then cutting power to the controller to test whether setting survive power outage (yes), and then hitting factory reset and checking. All works as described.