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I stumbled upon this website & hope you can help. I have a solar water system using a Goldline GL-30. It came with the house I have lived in since 2001. Never received any instructions on how to adjust it. I have noticed recently on cloudy days, my water temp is pretty average but the temp gauge on my water heater is about 100-110. So, when taking a shower, I have to crank up the hot to almost full. I have also noticed that the "Solar Collection" Indicator on my GL-30 rarely lights up which I believe activates the circulation pump. It would seem that the circulation pump should work more often to keep warmer water in lines. I am not sure where the "differential control" on the GL-30 should be set. My environment: I live in Maui, Hawaii where the average outdoor temp is around 85. We do get passing clouds from our trade winds but it only seems to be a problem water temp wise during our rainy season (Nov.-Feb.) when it can be quite cloudy. I have my water heater timer set for 3:00 AM - 10:15 AM and again from 5:00 PM - 10:00 PM, Mon. - Sun. Can you tell me where my differential control should be set?