I have a 2001 Sundance Optima (850) with a FLO message. The circ pump is running great, the flow switch tests ok, and the water level is high. I have removed the filter and made sure there are no blockages there or at the lower intakes. The controls and jets are fully functional, but the heater will not come on and the display just loops between the temperature, FLO, temperature, ICE. It is saying ICE since it dropped down to the 50's (not too worried about freezing here). Running the pumps does not get rid of the FLO message.

In following the wires, I see that the flow sensor is in serial with another sensor that lives on a circuit board in my heater assembly. I shorted that switch (J1 and J11 on the heater board) and I'm all good (FLO goes away and heater comes on). In looking at this circuit board, it doesn't appear to be connected to the heater in any way. The only thing connected to it are two small power wires from the main board and the sensor wires I shorted.

It looks like the replacement heater for my spa is 6500-310, which looks identical to my heater assembly, except it is missing the circuit board. Everywhere I see it sold, they say the circuit board is no longer necessary and has been removed from the heater assembly. So, anyone know what this board does? Can I stick with my existing heater and just stop using the board? I can easily bypass the board by just disconnecting it's power and removing it from the sensor chain.