Did you replace the probe? Are you sure the probe is below the water level? If so, sounds like the calibration is offWeird. I had a Ranco failure. It just went Blank and that was it. I had a spare all wired and ready to go. I did the simple install and the simple program to get it where I needed it. I set the Temp at 165 F. Differential at 5, H1. Done. Soon my 250 was boiling and steaming. I looked at the Ranco and it said 165 degrees. I took my infered thermometer and tested several spots and it read 210-214. The fan was still running so I kept clicking it down to see where the fan would shut off and I got all the way down to 100 on the readout and the fan shut off. I let it cool down and left everything until it fired back up at that 100 degree setting. the fan kicked on and I checked with the infered at it said 169 degrees. I guess my Ranco is off by 69 degrees. Yes it is on F not C. Everything has been working great all day but the readout is incorrect. Can anyone think of something I may have done wrong.??