Even after the thermostat shuts power off to the UTH, it continues to rise in temperature a little bit. It may take days to settle in. I would make sure I had a max/min thermometer, and really watch the max temp. I'd start low, say 81-82, and watch what your max temp gets to, and very gradually creep the temp up so your max is no more than 85-86. Like use two fingers and just _barely_ turn it up, then give it several hours to stabilize, then adjust again. I would check it multiple times a day, especially in the late afternoon when your house is likely to be the warmest.
This thermostat, while generally reliable, just had too much of a temperature swing for me and eventually drove me batty this November, causing me to buy four new Herpstat NDs, which hold the temp within less than a degree of what is set. Yes, they are expensive compared to the 500R but I just couldn't take it any more. The whole reason they are so much more accurate is because they are proportional thermostats, which means they vary the power supply to control the temp rather than just switching off and on. So the farther away they are from your set temp, the more power they deliver, and the closer to the set temp they get, the less power they deliver, so you don't have that several degrees overage that you do with an off/on, because the power is at only 10% as it nears the set temp.
