Simen,
No, not the thread I was thinking of. Must have it mixed up. But you are a man after my own heart! I had a controller similar to yours in my last solar tub at my old place. I had not only solar panels but also some loops through the wood burning stove that I heated my house with. SO the controller would sense if there was hot water at either the panels or the stove and start the pump. Also sensed if it was too cold and moved a little water through the panels to prevent freezing. HAd temp. sensors on the inlet and output of the panels and the stove along with an LCD display so you could see how many BTU's you were making, degrees per hour, all sorts of entertaining stuff. Down by the tub the temp was displayed with Nixie tubes.
I'm trying to keep this one simpler though. However, I'm already starting to think of improvements....
Jonathan