Differential analog solar controller-Elios Basic for solar heating plants: it compares temperatures of fluids in the collectors and the storage tanks and, when the difference is greater than DeltaT, starts the heat exchange through the pump. 3 temperature inputs from NTC sensors and 2 on-off relay outputs SPST. Additional thermostat for driving auxiliary heat source. LEDs show presence of power and pump activity. Configuration of 5 different system layouts. Adjustable antifrost function.