Yes, I'm referring to the small adapter board that the sensor plugs into. Did the flow light come on and the no flow go away? If not, push the button on the small adapter board until the no flow goes away and the flow light turns on, might take more than 10 seconds.
If this fails, then you most likely need a new sensor. One last try might be to remove the adapter board and plug the sensor in where the adapter board plugs into the main board. I'm still not convinced that the adapter board is needed, but that is up to you to try. I've been running my Aquapure without the adapter board flawlessly for 8 months. I was off and on getting the no flow error and this fixed my problem. The adapter board is supposed to improve the signal from the sensor but I'm not sure that was working as it should with my system.
I found this posted in 2011 about the adapter board, "The Tri-Sensor Adapter Board is NOTrequired for every existing installation, and only specifically addresses the service codes 172, 181 or NO FLOW. The Tri-Sensor Adapter Board does NOT provide a resolution to other service codes that may be present".