I recently baught a used 2003 Sundance Optima hot tub off a guy after it had set for the winter. I have replaced the heater, hi speed pump, and flow switch that we're cracked from freezing. But now I can't get the flo error message to go away to get the heater to come on. As soon as I turn it on the flo error flashes, then after a hour it will start flashing a plug error every time. I have taken the filter out and bled all the air out, and I can see that the flow switch is operating and has flow. I tried to bypass the heater relay to test it and see if the heater icon would come on but it doesn't. Does anyone have any ideas? Thanks!