Thanks for this great site/forums!
I have the J330 Jacuzzi and have had problems with it since the day my wife and I bought it. (Air buttons always breaking, 3 top control panel changes, 2 waterfall changes, 4 spinner jets replaced, 1 main control board replaced) *This hot-tub is the biggest POS I've ever bought, and will NEVER buy another Jacuzzi brand again. But however with that being said I am stuck with this hot-tub for now and we do like it when it all works like it should.
Anyways, I drained, cleaned and refilled it the other day as I always do about every 3 months and noticed that all of the sudden 2 days later the water was as cold as the day I re-filled it, and my first thought was "Oh NO, another freaking factory defect. and was about to drain the whole tub again and drop it off at Jacuzzis front headquarters with a note telling how bad I hate them... But after reading this forum about the heat issue others were having with this style and brand I thought well maybe I can fix it myself so I got right to work.
After trying everything else others had mentioned here, I removed the side and the main control panel and started looking and poking around and then I noticed the small (Circ) pump was hot and not spinning at all! My first thought was OK, I guess I need a brand new pump but noticed that the pump had a sales sticker on the side of it that was not from Jacuzzi but from Pool and Spa Depot were I had bought it!.. This was strange since I bought it "supposedly" brand new, but never the less it said the pump cost $219.99! So by this point I was boiling mad and was ready to try anything... So I took the whole pump out and took it apart completely, motor and all!.. Cleaned the inside and greased the moving parts and put it back together and re-installed it. I turned the main power breaker back on and wham, IT WORKED! the heat light came on after a few seconds and its back to running normal again
This only took me about 10 minutes and didn't cost a dime! WhooHoo.. YES!
So *IF you have this same POS Jacuzzi hot-tub it may simply be the little small (CIRC) motor/pump that is not spinning and just needs cleaning and greasing. Worked for me!