Same problem here. According to manual trouble shooting guide the control board is the issue. They cost hundreds of dollars!! I've had this heater for a few years now and it's nothing but a money pit. The only time it works is in the middle of the summer when I don't need it. Last year I had it worked on in May and then again in Sept. What a piece of junk.
Oh yeah, called Pentair today because I replaced the control board last year and thought it might be under warranty.......it turns out the warranty is a whopping 90 days. Not even whole summer in the south. The guy wanted to know if it was "out in the elements". What kinda question is that?? He was nice though, just no help.
By the way, mine was reading high so I bypassed the high limit switch. The display showed 76 degrees and the thing still wouldn't turn on. The manual leaves no doubt it's the control board. My question is, do you need the "kit" as listed in the parts section or can you just get the board??