Check your coolant level in the resevoir bottle and level in radiator, bottle should be filled to marked lines on the bottle , the coolant level sensor is inside the bottle, sometimes it sticks. You can blow very low amounts of air pressure in quick shots into the top 10-20 PSI(cover with a rag). Sometimes they stick and this helps, if not take it out and wash it out with hot water,check wires and connections and try again.