chartboy, i'm having the same problem and in same situation. bought my neighbor's calspa 2100 (manuf. in 2002) just this summer and now that temps are dropping to cold, mine keeps overheating (OH). I keep it on standard set at 100 (but have not used EC) and when i check it, it never reads above that but next time i look it has overheated. i've been following your discussion w/ pathfinder. i think i have my FC at F2, but will have to check again. it seems to run alot, but i keep thinking its just the heater compensating for the cold. not sure where the heating manifold is you have been talking about to adjust the switch...any ideas?