Hi,sorry to hijack the post, but my Serenity 5000G is doing something very similar.
About 12 to 18 months ago I had a similar problem, with my friendly local Hydrapool dealer wanting approx £800 to repair it!
so I ended up removing spa pack and circuit board, I took said circuit board to local electronics guy who repaired for me for £80.
replaced & has been fine since until now.
So now I'm getting: everything illuminated on display with light & pump lights flashing - then 269 on display - then r 2 on display - then LL 5 on display - then ---C with it clicking & trying to start - then it all repeats again?????
See Video.
any Ideas guys?
Hot tub fault.MOV