If you can open the unit, and lift the rubber button pad away from the pc board, you may find corrosion on the board, which can be cleaned away with denatured alcohol. A VCR repairman showed this trick to me, for repairing remote controls whose buttons no longer worked. I have a ceiling fan remote that had soda spilled on it, and requires this cleaning once a year or so. I haven't figured out how to get a permanent solution... I wipe the board and the carbon(?) pegs on the underside of the rubber membrane.