The COLD message was to indicate that your water was a certain degrees below the set temperature, or something like that.
The FLO is a flow error. Could be a bad flow switch, clogged filter, pump with an airlock problem, circ pump problem, etc.....
The FLO error tells the spa to keep the heater off because it thinks water flow is insufficient thru the heater.
This happened to me a couple months ago, and I got a new circ pump.
(Optima- somewhat similar to Jacuzzi, I'd think)