Release air for the Sand filter pump
When venting the sand filtration, first turn off the filtration. Then put the lever in the "N" position and release the vent valve. Close it again as soon as water starts to flow out. Unscrew the cap on the outlet or hose at the top. As soon as water starts to flow, screw it back on. Put the lever in the "filtration" position and switch on the filtration.