I have a York furnace, the last couple weeks I have been waking up to a 65 degree house when it should be 70, the thermostat says it should be on, but no squirells turning. I look at the board and it is flashing 7 times, which is ignition lockout, what is causeing this?

The most common cause, and easiest cure, is a dirty flame sensor. Remove and clean with fine sandpaper or steel wool.

KC3 I had the same Issue where my York gas furnace is blowing cold air and flashing red 7 times. I used your method as described, now my furnace is blowing hot air again.
Thanks for sharing your knowledge.

I did the same, I replaced the igniter and the fs. Flame sensor and still no good, I unplugged some wires and reconnect them by the gas valve and off/on and that would make it work for few more days, played with the sensor of air/in/out and it clicks so I know that works, wonder if it is the board.. the 2 items got replaced that everyone talks about, flame sensor, and ignition because while cleaning it I broke it few months ago.