After a winter of not using my Artesian hot tub, I noticed FLO on the display. Drained and refilled hot tub. Display now shows OH. I can put jets on manually but when it stops, display again indicates OH and water not heating. Repairman told me that there is a calcium buildup in heater which is causing it to shut down. I have very hard water, but also using stabilizer that may build up on heater when water temp. too hot when chemical added. I was advised that I need a new heater, which will cost $568, which includes $50 trip charge and $98 labor. Also, from the time I bought my hot tub, ozonator triped breaker when plugged in. I had to have it unplugged and am not able to use it. Repairman said that this would help my problem with the hard water and wants to replace the ozonator. Any comments?

I would like to see the heater that costs that much money, I'm sure you can call an internet site (877-936-2223) and get a better price on that, also a calcium buildup will slow down or even stop the heat but it will not cause the OH reading to appear when the pump is deactivated. Put your hand on the heater tube and check to see how hot it is when you touch it, it should be around the same temp as the water, if it says OH then it should be very warm/hot compared to the water when that is displayed. such being the case you either have improper water flow through the heater caused by either an air pocket (prime the pump to correct) or by a dirty filter (remove the filter and run for a while without), otherwise there is a possibility that your heater is stuck on and it may require a replacement of the PCB.
A likely cause of the ozonator tripping the breaker is that it may be the only 110V component that you have connected and your incoming power is wired improperly, this can be rectified by separating the ground and the neutral at the incoming power from the breaker, check your pumps and blower to see if they are 220v or 110v, if they are both 220v then this is a high possibility, if one of them is 110v then I would listen to the tech and think about getting it replaced, I would check with the same spa techs at the above # for a replacement Ozonator if that ends up being the case.