When plugging it in and turning it on, the only thing that appears in the display is the number 8 in the left l.e.d., pushing and holding the buttons does nothing, we've tried several combinations and still nothing beeps or changes the display. This unit was only used for 1 season and prior to installing it this year, we did the vinegar trick, the cell inside looks like brand new, no corrosion what so ever. Any help would be appreciated.