HotSpring Vanguard blinking red and green

[Spiderman]

Did a drain and fill today and now blinking red and green on 2007 HS Vanguard.  Circ pump is running well, all jets and light work.  I've re-tripped the breaker about 10 times and still blinking.  The green LED is on on the main board so Hi limit is good.  When I turn on the 30A for the heater a green LED illuminates on the heater board.  What's the first step in troubleshooting this?  Thanks!

[Spiderman]

So, the tub went to a steady red several hours after the drain and fill.  I flipped the heater breaker on and tub was at 102 this morning.     Problem fixed for know, but I'm guessing either the pressure switch or the fact that it was a cold weather fill.  It was only about 36F when I filled her up, but I though cold fills only affected the hi-limit? 

[Spiderman]

Problem resurfaced so I did a little troubleshooting.  I jumped the pressure switch terminal on the main board with an alligator clip and tub is working again and heating.  It's what I thought, the pressure switch so I guess I'll be ordering a new no fault heater.  (Don't worry.  I pulled the alligator clip and left the tub with blinking lights.  Circ pump is still going)

[Jpoker]

My vanguard did that each time I filled it. It is an airline company in the line. Not enough water flowing past the heater and it over heats and trips. The heater circuit uses the filter with 5he grey cap. I removed the filter, unscrew d the tube and added my own adapter with a quick disconnect for my fill hose and I fill the spa through this and not just in the filter compRtment. It purges all air and i never had 5he problem again.  Just FYI