I have one of those. It's definitely just a pull straight out to get it off. Just hook your fingers in the top by the on/off switch and pull. It's held on on the four side corners just above and below the air vents on the sides.
Thank you for replying. Mine was really stuck firm but I was able to gradually pry it open using a sharp strong knife earlier, screwdriver wouldnt even go in. May be the plastic had shrunk over the years never having been removed. Im trying to see if I can add remote controlled switch to it so that I can start the heater without getting out of bed after cold nights.
