Did it run out of fuel?
If it did and you put more in, Check the fuel filter. Also check the Thermostat setting. It is not uncommon to have the dial Vibrate to a lower setting. If that happened you can fix it by pulling off the knob and installing 2 small O-Rings on the shaft and stick the knob back on. The friction of the O-Rings will stop the Temp knob from moving easy again.