2nd cook - thermometer issue

twlangan

Grilled a sirloin tip this afternoon - turned out excellent. I did a reverse sear and my only issue was I left it on a bit too long (90 seconds each side) and charred it a bit more than I liked.

Now, here is my issue...  I cooked the roast low and slow at 250F. Pulled the roast, removed the plate setter, and opened the vent to let'er rip. Closed the dome to make her build heat and the thermometer rose to 200F (it had dropped when I was removing stuff) and then dropped to zero, even went backward past zero just a bit once. The Egg was roaring hot - had blue flames licking around and coals looked like lava. I put the roast on to sear, closed the lid, thermometer went to about 100F. Opened it to flip the roast, closed it again, same reading. After the sear, I opened the dome to remove the roast, closed the bottom vent, removed my meat, and closed the lid and put the rain cap on. At that point, the needle immediately rose to 600+. I have no idea what was going on. Now I am wondering if my thermometer is any good at all, if the rapid rise in heat "confused" it, or what? I calibrated it when I assembled the Egg - it was off by 10 deg and acted just fine until this. Has anyone seen this before? Should I request a replacement? Do you go to your dealer or contact company headquarters? I am a bit leery about planning another cook not knowing if the thing is going to work - figure I had better have a plan B. Will probably remove it and try the boiling water trick to see what happens first.