The BURST Toothbrush does have a built-in quad pacer timer, Which means you will feel an intermittent pause every 30 seconds to tell you to move quadrants in your mouth and after 2 minutes the BURST brush will automatically shut off.
If the BURST Toothbrush or Water Flosser is still turning off the First step with the Toothbrush or Water Flosser is to try a reset on your BURST Water Flosser or Toothbrush. This is done by plugging the unit in to charge, Once charging go ahead and hold down the power button, After a couple of seconds all of the lights will illuminate on the unit. You can then release and the lights will go off after a second and the unit will then start charging. Let it finish the charge and use the unit as normal.
If this reset has not resolved the issue then take a quick 5-10 second video of the issue you are having and submit your warranty claim through the BURST website here: https://www.burstoralcare.com/register
A video on How to reset your BURST Toothbrush: