Hello, I found this post describing exactly my issue. I kept having my hot tub "trip" every few weeks and then it started happing every other day until it finally went out. I would turn flip the breaker and within 2 minutes it would click off, show the code D17 as described above and only run the circulation pump.
(Back story- I have already been running the tub without the ozone as it is 20+ years old that I inherited from a neighbor who "had it running a few years ago". When I had it moved from his yard to mine, I also ended up inheriting the carpenter ant nest that was inside the tub foam! Needless to say, my wife wanted it taken to the dump and I had just started a contracting business so I said to myself, "If I can't fix this issue, what kind of contractor am I!" We flipped it over, killed the nest, removed the damaged insulation, completely restructured it, refoamed it, re-sided it, flipped it over and filled it up. It worked great for about 6 months. End of back story)
I then assumed it was a heater malfunction that was overheating. I put my hand on it and it would get very hot then shut off. I ended up finding a ($300) replacement heater with an exact match to my current 25 year old tub and swapped it out only to find that it didn't fix the issue. I was about to call a hot tub technician until I stumbled onto this forum. After reading these posts, I went to try and follow the blockage theory first. I have 5 filters in the tub and the one closest to the pump was the one with the issue. As I was unscrewing the top, what seemed to be an air pocket released. The circulation pump reacted by running completely different right away. After resetting the breakers, it's been warming up ever since. Although this may not fix Homer14's problems, it solved mine and I hope it helps some one else in their search for the solution.
My concluding assessment. The heater was overheating due to an air pocket causing the system to trip (I had primed the lines with good water flow and made sure there were no obstructions when installing the heater).
Thanks!
