OK...maybe I got confused about the OP question. The Tstat will always have to be higher than the temps in the tub if you have the probe on the heat sourse. That will be the case with whatever brand Tstat you use. I thought she meant she sets the ranco on 98 and the actual reading on the ranco was 93. Maybe the OP will clarrify exactly what she meant. If you have the differential set at 5 and the probe on the heat sourse you will have to set the Tstat 10-20 degrees higher than the temps in the tub.