I had a "no flow" error on my Auto Pilot and went on a goose chase trying to resolve it. Posting the resolution here so you can learn from what I went through. You won't find this on AutoPilot's website and I don't think this resolution has been posted anywhere on the internet. I searched pretty good. This applies to other chlorinator syetems as well that use a sensor to detect flow.
Received the dreaded "no flow" alert after turning back on for the season. Checked the union valve screen. It was clean. Cells looked clean but went ahead and cleaned them again with water and acid according to Auto Pilot. Checked to make sure the system valves were all in the correct position. Reseated the tri-sensor cable. Ran the self-test. Prayed. Nothing resolved the problem, still have no flow alert and no chlorine production.
Spoke to Auto Pilot and they recommended I clean the union screen. It was spotless. They recommended all of the above which I had already done many times. Still no flow. Auto Pilot suggested my out of warranty tri-sensor was defective/bad or possible a circuit board needs to be replaced which would cost me big $$$.
Then in the middle of the night, after wondering what I had missed or could be wrong, I figured it out.
The tri-sensor's flow sensor was not being hit directly perpendicular with flow.
The tri-sensor is very sensitive and must be installed in the manifold precisely perpendicular with the flow. If it's off by just a few degrees, it could indicate no flow. If you have this problem remove your tri-sensor from the manifold and reinstall it as close to perpendicular as you can get it keeping in mind it can shift a few degrees as soon as you get close to tighten. This is likely to solve your problem without to replace expensive parts.
If you run into this problem, let me know here if this resolved your problem. Curious to know who else has run into this.