High temps on Smokefire

[drjtcase]

I have a Smokefire EX6 that is about three years old and has been quite reliable until the last few months. I keep it clean (clean after every two or three cooks), but recently it has been very unreliable in the temp regulation. On a recent brisket cook, set the temp to 225F. Checked the temp after 4 hours and the internal sensor said 225, but a separate sensor read out at 275F. Turned the temp down to 200F and the internal sensor reads 200F but the free probe varied from 218 - 260F. Could it be that the internal sensor is not working correctly; not clean? I was trusting the internal sensor al this time, but now worry that it is unreliable and if so, whether the overall temp management is messed up.

Thoughts?