I've been only having this problem in the colder to winter months. My heater works like a champ in the summer, but as soon as it gets to be around 30 degrees my fan in my heater stops moving. I have to knock it a few times to get it to turn on. It's getting to be pretty annoying because even if I knock it 10 times, the fan never seems to get to full power. I've heard of taking the heater out and greasing up the spot where the fan meets the motor, but I asked my dad and he said "NO WAY, there's shouldn't be grease there!" Any suggestions?