Hello,
I have a York P1CK D1N06401A natural gas furnace in an upflow orientation. The equipment is 11 years old and has all original parts and controllers. The LED fault code is 8 flashes which, according to the Installation documentation ("Indicates that the flame has been lost 5 times during the heating cycle. This could be caused by low gas pressure or a faulty gas valve"). I have my doubts about either of those two things being the case based on the manner in which the lockout is occurring.

The ignition sequence goes as follows:
Thermostat calls for heat (with fan control set on 'Auto'); The circulating blower is energized instantaneously (and remains on continuously even after eventual lockout); The ignitor begins to warm and glow; 17 seconds after call for heat the gas valve opens and ignition occurs; After 7 seconds the gas valve closes and flame goes out; After 17 seconds the gas valve opens for a second time and ignition occurs for the second time, the valve stays open for 7 seconds and then closes extinguishing the flame; This repeats 3 more times until the unit locks out at the end of its 5th attempt; After 60 minutes the controller unlocks and allows the ignition sequence to occur again, but again it goes through 5 cycles and locks out.

I don't think that this is the way the unit would behave if the flame sensor was malfunctioning and to test it I disconnected the sensor in the middle of one of the seven second periods where there was steady flame. The unit then acted as though it saw no flame and waited 60 seconds before an ignition retry, went through 3 cycles and locked out (instead of the repeating 17 second cycles and lockout after 5 cycles). I reattached the flame sensor and the unit went back to displaying its 17 second cycling.

For some reason the controller seems to be treating the shutoff after 7 seconds as though it is a gas interruption occurring in the middle normal operation.

This one has me stumped, I hope someone has some better ideas than I do. We' re looking at 10 degrees tonight with 50mph wind gusts (could get chilly if I can't get this thing going).

Thanks.

You seem to have a flame sensor problem. If this furnace is the one I think, as I am not as familiar with model #'s on York, you should be able to fix is quite simply. If you feel comfortable, get some fine sand paper or emery cloth and clean the flame sensor by stroking it lengthwise away from the base toward the tip. It will probably have to be removed to accomplish this. Check wiring from the flame sensor to the control board to locate any irregularities. It should work.