I have a Carrier MODEL 58MVP 90% effiecient furnace and live in Minnesota. The furnace wiln not come on when the temperature is very cold outside. Our house was 47 degree's the other morning when it was 25 below outside. Then all of a sudden it starts working. The fan will work when it is on the auto fan mode but the furnace will not fire. I called a heating company and they advised to check out the code when the furnace is not heating and that code is 4 green blinks and one yellow which shows ignition lock up. I called the heating people back with this info and they replied that I need to call them when the furnace is not working. They cannot find the problem when the furnace is working. I have checked to make sure the PVC pipes are clear on the outside of the house etc.

Thanks Rich