I just fixed my low heat problem on my Amish Country Spa. The heat would not get above 96 degrees. After eliminating the possibility of a restricted filter, I looked at the thermostrat. I found that there is a loc-tited allen head adjustment screw on the thermostat, regulating the shut off temp. My internet research told me that 1/4 turn equals approx 5 degrees on this model. I went 1/2 turn clockwise, and now I am at 105-106 degrees at maximum temperature. Good enough. I backed off a little on the topside temp control to drop a couple of degrees. I found out that this issue is common after about 5 years of spa use on non digital models.