Helithumper

I forgot to mention. All the functions are working becides the heater. All three pumps and lights are working as designed. So not sure what else could set off the fl1 code.

Hi I'm new to the forum. One of our clients gave us his 2005 sundance spa palermo because the were never using it. The owner of the tub said that it stopped heating So I have installed the hottub and replaced the heater and I still have the flashing fl1 code. I can see the flow switch and it's working properly. I've also checked and I have contenuity when the tub is on. The circ pump is working as well. I've filled the hottub with a garden hose in the filter tubes to eliminate an air lock. I've also run it without the filter. What am I missing? Can it be the circuit board. Thanks dave