I finally figured out that my FL1 error is due to my flow switch. When I remove it from the pipe and press the magnetic head to close the circuit, the FL error goes away and the heater works. However, when I insert it back into the pipe with the arrow facing the same direction as the water flow, the error code reappears and the heater does not work. Any tips on how to screw in the flow switch back so that I can reset this thing? I have Sundance Caprio with Harwill Flow switch. Thanks in advance.

sounds like your circulation pump is the problem not the flow switch

try running it WITHOUT filters - the most likely cause of flow errors is blocked filter cartridges

on a sundance caprio the filter won't cause this problem... sundance has a bypass in the filter compartment so even if the filter was 100% clogged, it would still have a source for the circ pump. The filter problem is more common with the cheaper lines of tubs.

thats not correct - a caprio uses a double ended cartridge - one end for circ pump, the other for pump one. this is the sole source of suction for the circ pump on this model. (at least export versions anyway.)
Regardless of brand or model, THE most common cause of a 'flow' error is blocked, or dirty filters. Therefore, removing and running the spa without the filter in place (make sure no debris can be sucked in) is definetely the first , and easy thing to do to eliminate the filter as a cause of the problem.
Even in spas with filter bypasses, the suction through the filter is usually the primary source and a blocked filter can still easily cause this error

I must be the lucky sundance owner with the design that uses the bypass.... never had any problems even when the filter was so plugged that when you kicked on the high jets the filter literally collapsed on itself.

Keep in mind I am only going by experiance on the 3 sundances I've had, one of them being the caprio (mid 90's) along with the cameo (94). I'm sure there are probably different designs out there by now.

Capri - maybe, Caprio only since 2000 and has a laing circ pump for heat/24 hr filter as well as 2 spd pump one

Well, by now you probably fiqured out the problem hopefully I can get my Tango heat to work. I had an FL1 error code cleaned the filter and the check valve and still had the same problem. It wasnt untill I saw a small secondary filter that fit in the pipe towards the circulating pump floating in the wier basket. This was the cuase of the problem as it was totally clogged, it looks like a cap the size of a gatorade bottle with a very small nylon mesh screen.* Note the owner's manuel says nothing of this.

After that everything worked fine with no error code.