Below are photos showing what to check if the pump on an A53 or Vivaldi stops engaging when tapping the one cup or two cup button. This is useful if you are still getting flow out of the group head but if the pump does not turn on.
Before doing this tap the one cup button in a quiet room and listen to hear if the pump is still quietly "wurring" but if it is not turning the pump. If the motor is still "wurring" but the pump is not creating pressure the issue is likely a pump with a divot, causing it to be unable to prime. You will likely need a new pump if that is the case.
Before doing this we recommend unplugging the machine and allowing it to cool off. At this point remove your back and side panels - instructions here.
Once the panels are removed check the electrical connections shown in the photos below.