Gas York Model# P9MPD08N04801A about 18 yrs old Before starting this, please let me tell you I am an electrical apprentice, and by no means an expert on gas furnaces. Issue I am having is it seems to run SOMETIMES. Then I get the 4 flash (OPEN LIMIT) code. I have changed the filter so this is not the issue. I cycle the power to the furnace and this seems like it used to work but not anymore. I initially thought it was my limit switch, but it seems to be working fine as it is closed (reading 0V accross terminal, or 24V from terminal to ground on each side). Then I thought it was the rollout switch, I shorted one of them out and it was working perfectly, however after sometime went by (10hours or so), the 4 flash code would come back. When the furnace does not start, it gets the "error code" BEFORE any flames are made (igniter is not lit up) This code seems to come up before the igniter turns "red". I do not think the igniter is the issue because it does work "sometimes" as I stated above. Could it be the gas valve? If so how do I test this? Any other ideas? Thanks! EDIT: I should add, I believe I only have 3 roll out switches, and I am unsure where to find the 2 aux limit switches. Those can be the issue also... [IMG]http://imagizer.imageshack.us/v2/800x600q90/543/3q1k.jpg[/IMG] [IMG]http://imagizer.imageshack.us/v2/800x600q90/838/z8px.jpg[/IMG]

In morning/every morning the inducer is running but no heat. After furnace off for a few hours the unit doesn't ignite or even spark when the thermostat requests heat. The inducer is running but not spark. If I cycle power the system works fine 100% of the time. If I remove, reconnect pressure switch hose at exhaust it starts working. I already replaced pressure switch