You need to contact a hot tub technician/engineer as you clearly have issues.
'ICE' means that the water temperature is too low and therefore the pumps will be turned on to prevent freezing within the plumbing. Depending upon the spec and settings, the heater maybe disabled during 'ICE' condition.
'ECON' is Economy Mode. If you have a mode button, keep pressing it until you see 'Stan' on the display. This will put the system back into the standard mode.
'FLO' means that there's insufficient flow of water through the heater, or non at all. 1) Check the water level - top up if low. 2) Ensure that all jets are open and flow water - if they don't you may have a pump issue. 3) Remove the filter(s) and see whether or not this clears the fault, if so clean or replace the filters.
'COOL' is displaying because the set temperature is much higher than the current water temperature.
As I mentioned at the start, you really should get someone to take a look at your hot tub. You may have a few issues that need resolving.