so, pump is finally running! Upon closer inspection of the pump's connection box, I noticed that the plastic on a component on the circuit board was chipped off, which led to the suspicion that the electronics were not functioning properly and therefore the pump was not running. Unfortunately, Grundfos does not offer service for end customers and I could not find the connection box as a separate part, so I bought a complete new pump... Now I just connected the new connection box to the existing pump and behold, the pump is running! (It is audible and palpable, plus the temperature at the solar collector dropped significantly and quickly, which leads me to conclude that circulation is working.) The control now works too; if the ESR does not send a signal, the pump no longer runs! What I find strange, however, is that the float of the flow meter installed below the pump still does not move! Could it be installed the wrong way around? As wrobel correctly pointed out, the pump must be on the return line. However, I am confused that the line above the pump (i.e., the return from the roof) becomes noticeably warm and the supply line at the Delphis-solarstation has no hand-detectable warmth! So maybe the pump is incorrectly installed in the supply line after all and was possibly damaged by the excessive heat of the water, or the pump is installed backwards and pumps the warm water from the roof toward the storage instead of the cold water from below upward? (which would then correspond to the functioning of a supply line, right?) The installer was apparently quite an expert in his field... -.- Judging by the previous owners, it was probably supposed to be as cheap as possible, I wouldn’t be surprised if the system never worked properly and no one noticed (the owners rented out the house before selling it)... Thanks in advance! Regards