Hello, I'm late to the game here, but our Vanguard V (circa 2006) also is not heating properly. Cool day yesterday and I jumped in waiting for the wonderful heat that was barely there. My time didn't last long. I flipped breakers off & on. Checked temperature setting (at 102 F). Tonight, all I can see is the red light on the spa from my window here.
I would greatly appreciate any suggestions.