My hot tub keep cutting off and displays the OH. The tub is about 15 years old. It is not even heating up to the temp setting of 103. It will run a couple of hours then shut down with the OH on the display. When the temp gets close to 100 it shuts down. I have checked the filter and cleaned it. I have opened all the valves, the pumps are working as it should. I replaced the heating element with a heavy duty one about 4 years ago. I have cut the breaker off several times to see if it would reset itself. The temp was 98 and it cut off with the OH on the display and will not to anything even when cutting the breaker off and back on still displays OH. I don't know what to do at this point and any insight would be helpful.