F3 is shown after a high level alarm has been activated and then returned to 'normal'.
The F3 indicates that there was a high water level previously in the pump station that it caused the AlertMaxx2 to signal high water (F1). When the level returned to normal, the F1 changed to an F3 and the alarm mutes.
The F1/F3 error codes should be investigated, as it shows there has been a previous issue with the pump station (i.e. pump 1 may have failed and caused the water level to exceed the high level alarm float).
Please call 0330 9000 999 to arrange an engineer visit at a time that suits you.