We all have read many times on this forum, on Amazin' Ribs and elsewhere that factory thermometers are not reliable. It has been drilled into our brains so often that we think nothing of shelling out big bucks for TelTru, Thermowerks and other premium thermometers. So, I thought I would test the lid thermometer on my Weber Performer Gen 2 2005 that has been used a lot since I bought it new. I pulled off the thermometer and placed the probe into boiling water. To my great surprise, it read dead on at 212 degrees!!! I repeated the test several times and each test read 212.
Now, I don't mean to bash the need premium thermometers, I own many and rely on them. The Thermowerks with cable probes are wonderful for checking temps at various levels and various places in my cookers. But I have newfound faith in my the Weber factory thermometer. Check yours and let us know how accurate it is. It would be fun to get a few samples for reference points and discussion.