Thermometer Stuck during BIAB MASH

[quaboagbrewing]

The solution to this may be just to manually check temps with a traditional mercury style thermometer but curious as to the potential cause. I am doing BIAB in an 8 gallon kettle and have a threaded thermometer in the top port. Prior to brewing I verified the thermometer was accurate by comparing against 2 mercury thermometers to make sure all 3 match. Got my strike water to the appropriate temp and then mashed in. This was a 2 step mash starting at 141 and then going to 153. After mashing in the thermometer reading stayed right at 141 for the 1st 30 minutes and dropped maybe 1 degree by the end of the 45 minutes. I happened to have the Mercury thermometer still handy and inserted into the Kettle and I was getting a reading that was about 4 degrees lower then the kettle thermometer. Had same issue going in the other direction. Brought the mash to 153 using the Mercury thermometer to check temps and when the Mercury thermometer read 153 the kettle thermometer was still sitting in the low 140's so for some reason it's getting stuck. Doing BIAB so all the grain is in the bag and wouldn't expect that anything got into the port with the thermometer so not sure why this is getting stuck. Bad thermometer? Also wondering if could be an issue if I don't have proper shielding between the outside of the thermometer and the burner....maybe getting too hot and causing issues? For now I'll just not rely on the kettle thermometer but would really like this to produce accurate readings. Any thoughts as to cause and remedy??

 

[brick]

This is going to sound dumb, but have you tried tapping the thermometer? (I'm assuming it's a dial indicator.) I spent a few years in university laboratories surrounded by dial indicators of all kinds and the first thing I learned was not to trust one unless I'd given it a tap or two.

 

[Biscuits]

This is going to sound dumb, but have you tried tapping the thermometer? (I'm assuming it's a dial indicator.) I spent a few years in university laboratories surrounded by dial indicators of all kinds and the first thing I learned was not to trust one unless I'd given it a tap or two.

^ This. And as a rule, I remove it every 5-10 minutes and reinsert it, this way the dial is forced to move without beating on it too much.