I purchased a used jetsetter (1992 J model?) last year and it worked great up until last fall. I drained and cleaned the spa, refilled it and upon refill noticed that the spa was not heating the water. I phoned a friend who repairs them and he instructed me to try to remove the filters and call him back. The spa heated up and I was back in business. I reinstalled a new set of filters. Now it seems to be doing the same thing (not heating unless the filters are out). I was wondering if there's a flow control switch that's sensing restricted flow and shutting down the heater? I dont see one or anything that resembles one in the equipment compartment. I'm a newbie to this forum but I've owned a few spa's that I've repaired and this forum had a lot of good threads that helped.
Any suggestions or comments would be greatly appreciated, thanks!
ps. I've attached an image of the spa guts as a reference.