The actual switch is probably built into the board and the button you see is just a cap that you use to press the switch. The cap could be out of spec so the problem would be resolved by replacing it. Another possibility is the board has slipped off its mounting. A third possibility is a defect in the switch on the board. A little bit of play, that might also allow some rattle, helps guard against the cap getting wedged in the fire position, something you don't want. If the button isn't working consistantly 99,99% of the time and the mod is new there's a defect. The seller should be anxious to make good. Nobody should want mods with bad firing buttons out in the wild.