Hi I am new but I have an older Beachcomber hot tub, I think it is a 500 series. The display shows FL on occasion but all I have to do is push down on the filter and it goes away. What might be the problem, I have a new filter. I am worried about cold weather coming soon and if it says FL it isn't flowing and could freeze. It costs a fortune for the tech to come as we live a distance away so I need to try and fix this myself. any suggestions?????? could it be the flow switch and if so is it easy to replace??