Pool and Spa
Questions about Pool Repair? Ask an Expert Online.
You are correct in that if you jump across the terminals for the flow switch and heater comes on then it is indeed the flow switch, now be sure you have the new flow switch in the correct flow direction, a flow switch has a metal pin and a round probe on it and when installed in the see through "T" the metal pin need to be towards the heater outlet also in the flow switch itself there is a small arrow showing water flow direction.
If all this is good then you have a defective flow switch and you will need a new one.
Not that I have ever seen, once you said that you jumped across the two small pins on the circuit board where the flow switch plugs in and you had the heater come on I ruled out the circuit board as I have seen a bad board cause the FLO code as well I have seen a bad pump or just a clogged pump cause there to be not enough water flowing through the switch to make it close, if you do not see water flowing through that "T" and the metal pin does not move right then you have a pump issue either the pump is dead and not running or you may have debris in the impeller inside the front housing so you would need to remove the front housing of the pump and inspect the impeller for clogs then re-assemble and turn breaker back on.