EDIT: just a reminder that any power tool can bite you if your not careful. After a couple of years and many hundred of hours of print time the hot end heater and thermistor on the hot end of my low budget printer came loose and started flailing around on the print bed. And with the thermistor flopping around in relatively cool air it kept telling the heater to get hotter. ...the perfect thermal runaway scenario. Of course I wasn't home to keep an eye on it at the time (stupid move, I know better now). Fortunately my wife came home early and smelled the smoke and shut it down before things got worse. I just finished the post-mortem on the printer and I'm starting the long list of improvements I'm going to make on the next one. The silver lining to the whole mess is it scared my wife just enough to free up some substantial budget for my next printer build. The fuzzy gunk must of been the last of the filament to come out while the heater was working loose. You can see the burnt areas and smoke stains on the part. Things could have been much worse.