Hi all. I've been getting the Heater Error message on my UM2 lately as well. I had installed the Olsson block a couple of months ago, and I've had no problems whatsoever up until last week, when I got the Heater Error for the first time. I noticed that the temp sensor was loose inside the block (I pulled it from the back and it came right off), so I tightened the screw on the block and I thought my problem was solved. But the next day, after about an hour into the print, I got the dreaded Heater Error message again. This time the sensor was firmly fixed inside the block. I've been using izzy's shroud (https://www.youmagine.com/designs/um2-fan-duct-v2) and the stock 25W heater. Help!