Hey out there, new guy says hello...
OK, now the important stuff
A flashing FL1 on a Sundance spa usually is caused when the flow switch does not close when the small 24 hour pump is on. This is a dangerous condition because the heater could over heat due to the lack of water flow though it. Here's a pic of the very common flow switch -
See the little round "lolly pop" on the right? That has to move and touch the round post on the left anytime the spa power is on after the initial start up sequence. If it does not you get the flashing FL1
My problem was after buying a used spa and having it delivered I was getting the flashing FL1 Looking inside the pump area, I found that the large pumps are not mounted firm to the spa base board, but "float" with rubber feet attached to the pump base plate. When the spa was moved, it was done with the pump cavity facing down. This allowed the clear 3/4" hose that feeds the small pump to fall under the large pump. When the spa was set back down level the large pump base came to rest on the clear hose and flattened it. As soon as I removed the hose from under the large pump the problem was fixed. So, this is easy to check on your spa. Just remove the pump area side panel. Follow the 3/4" clears hose(s) back from the flow switch and make sure they have not gotten under the a pump. In my 2005 Palermo, it was the large pump on the left.
I hope this helps some of my fellow spa users...
Dane