Watch the distance!
I had a solar hot water system installed, and it came with one of these controllers. The controller runs the pump for thirty seconds every half hour to see if its worth running the water through the solar collectors or not. However, the installers put the collectors so far away from the tank that thirty seconds isnt enough to get the water from the tank, up to the collectors and back again. So, the system always decides its not warm enough, and so never runs, and so doesnt save any electricity.
The thirty seconds is not adjustable on this product, so I have to find another controller that will allow me to adjust the timing.
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