First I think we need some more info like were do you have the probe how is the rack set up and which tub is the probe in. Have you tried sampleing the heat at diffrnet places on the flexwatt? Do you get drafts in the room and is the rack on the ground and what type of sub floor do you have? Where in the house is the rack near a window or an outside wall. You are getting something that is causing that thermostat to constantly adjust the temps. Maybe the snake is laying on the probe?