The recent heatwave has brought a whole new bunch of problems. The extruder motor, it sits right above the "Hot Bit" of the extruder, became overheated, what happened was that the filament was softened by the high temperature, instead of sliding neatly down the guide tube, it wrapped itself around the drive gears, and tucked itself into any space it could find. I had to dismantle the extruder in order to clear the jam. This had a "knock on" effect as rebuilding the extruder meant that the Z axis had to be recalibrated. This took a couple of hours, fortunately the printer carried on working after the rebuild, and the current print of a Piper Cub J3 with floats was resumed. I managed to keep the printer working, by putting a fan salvaged from an old power supply, close to the extruder. This kept things working, and no jams happened. I checked the Prusa website for extruder motor cooling mods, and found one! The mod is a cowl that fits over the motor, takes a 40mm fan, and costs less than £20 including postage. Should get the bits before the weekend.