Crazy Temp Jump

[shadricko]

This is my 4th time using my new PB series 3 Electric smoker, and I've had no issues thus far other than difficulty reaching temps above 270.
Today I'm trying to keep my attempt at an even 300, but once the temp gets to 300 and the element kicks off, the digital thermometer on the unit immediately jumps to 530 degrees and lingers there for several minutes before rapidly descending back down to 250.
Then, the cycle repeats. Element kicks in, reaches 300, element kicks off, temp reading jumps within seconds to 530. I know these readings can't be accurate, but I'm not sure why it's happening.
Any ideas?

 

[MikeInFla]

How low do you have the cap? At higher temperatures you need to open the stack high. Also make sure you have water in the pan.

 

[shadricko]

It's electric, so there are a couple of vents in the back, and they're wide open. Had and still have water in the pan.
I dropped the temp to 225, and it's been holding steady for a couple hours. There's been no more than a 15 degree swing as it cycles.