Why isn't the countdown timer starting after I press START/STOP?

The timer will not begin counting down until enough pressure has built up inside the cooker. If the counter hasn't started after a reasonable amount of time, it typically means one of three things: you haven't pressed START/STOP (the indicator light will still be flashing), the gasket has not been fitted properly into the lid, or there isn't enough cooking liquid in the pot. (Page 19)