Hello !
After seeing that water was not as clear as in its original state, I decided to replace it. I did all operations carefully in order to not have water leakage on the floor. First, I unplugged all the sytem from electrical power.
1 - I closed the two ball valves at the bottom of Aquaduct, I opened the circuitry just by removing the hoses from the two connectors. I emptied the circuitry.
2 - Then, it was the time for the Aquaduct. I open the two ball valves and with patience and care, I tilted the Aquaduct until not having water leaking from its input and output
3 - I reconnected the complete circuitry, I filled Aquaduct on the right side as always, put the power on and...
The pump is rattling and I observed that I have no flow, few seconds later the series of long beep. I checked again the ball valves which are open. No matter. I tilted Aquaduct several times but no improvement. In order no to damage the pump, I did my trials very fast.
At last, I connect a short hose on the input of the Aquaduct. After power on, it appeared with a finger on the other end of the hose that I have no succion. I really don't understand.
Thanks a lot for your help. I checked any thing I would forget but all is ok...

OK, I succeeded in fulling my circuitry. It appeared that for a system full of air, waterflow is very difficult. With patience and several restarts, it works. A tip : don(t hesitate to shake the hoses themselves.

Tilting my computer is a difficult operation due to its weight.

Zitat

These pumps do NOT pull a suction, you always have to have a positive head pressure for them to work... they only 'push' water through the circuit.

Very important information to keep in mind, thank you. To detect any succion with the finger is not a way to verify if the pump is operational, ok...
Another question, maybe stupid, but I want to check this point. We have black and red little plastic balls inside Aquaduct. By tilting Aquaduct, do we have a risk of having these balls escaping and running in the circuitry, or the conception is safe such as we cannot have such a problem ?