Just started my hot tub up again after it was closed for the winter months and I keep getting a "FLO" message. Have tried purging the lines for air pockets, replaced the older filter, made sure all the valves are open and water level is fine. Main pump and jets work but no heat. The secondary pump(circulation pump) doesn't seem to be doing anything but "humming". The filter chamber doesn't seem to be pressurized either(ie. no air/water escapes when bleeder valve is opened.). Anyone with a suggestion?

replace circulation pump