Curse the Red Blinking Power Light

[Doctorhawaii]

2005 Vanguard Problem:  9 months ago I started getting the blinking power light/high-limit tripping and no heat problem. Checked the circ pump and the filters and they seemed good. Checked the sensors, they tested properly. The heater seemed good and didn't have any hot spots. It would reset just fine and everything would work great after a reset, but only for a couple of weeks. This same scenario went on for months, until the relay board cooked. So, I replaced the relay board with a new one. All worked well for...a week, then back to the blinking light and no heat. So, I replaced the heater and sensors. Everything worked well...for a week, then the no heat blinking power light again. So, I replaced all 5 filters. Everything worked great!  For two weeks. Then, the same damn thing, no heat and the blinking power light. So I've again had to reset the breakers to get it back to life, which works. The circ pump seems fine, I get good ozone bubbles and the waterfall flows great. What in the world is going on??? The only things left to replace are the circ pump and the motherboard. Why??? Anyone have any new ideas on this conundrum?