So after having some beers finish at a higher gravity than I planned on, some being sweeter than planned, and every single Extra Stout I brewed stop at 1.032, I now realize the ugly truth. I believe some of you on here suggested I was mashing too high and maybe my thermometer was off. My thermometer is accurate, and 156 isn't too high of a mash temp... however, you were still right in different ways.
I got to thinking maybe the top of the mash is cooler than the bottom, even though I stir up down and all around. So I got a lab type thermometer and tested it against my digital tonight. The lab type is quite a bit longer. I tested them both at room temp and heating my sparge water and they were exactly the same.
I then mashed in, stuck in my digital and stuck the lab type down as far as it would go and I could still read it. Here are the results...
That is pretty much a 10 degree difference! No wonder my FES was getting stuck - I was mashing at 166!
So, I wouldn't trust digital unless it's got a long probe. 3" just can't penetrate enough. You're going to need at least 8"
By the way, I have always used BeerSmith to calculate strike temps. My first 2 or 3 brews I used my friend's long dial thermometer then switched to that digital one.