I have a ducane furnace model cmpe100u4b that is not always igniting. Led will read normal then trip to a code call for heat (fast heartbeat) while the furnace clicks into and throughout its heat cycle.
Any ideas


(I already had to change the fan limit switch and inducer motor).

You might clean the flame sensor if equipped.
Look on the back side of the blower door to see what the blink code says.

The code says it is calling for heat. The inducer motor was running for a long time before the furnace actually ignited. (alot longer than it should.) Someone else said it might be the pressure switch not working correctly. That part is ordered and under warrantee. Any other ideas would be great. Thanks