This issue most likely occurs after replacing a filter due to air inside the filter housing getting trapped.
If your AquaTru takes a very long time to filter one tank of water, or if the water in the tap tank seems warm, see Slow or no flow.
Otherwise, try these steps:
Turn the unit on. Make sure the tap tank is full and the clean water tank is not full.
Lift the clean water tank off the base a few inches.
Put the tank back on the base and the unit will now start. Repeat this up to 5 times if the unit stops again during the filtering process (the expected outcome is that the unit will not stop and continue to filter normally).
If this does not resolve the issue, please contact Customer Support and they will determine if your unit needs “air bubble troubleshooting.” If it does, they will walk you through the steps. If this does not work, you will need a replacement base.