[jason92s]

10 year old York 80. First problems were traced to some material stuck in the tube that attaches to the pressure switch. The unit would start to kick on then just stop. I cleaned it out and it worked good for a week. Then started doing the same thing and I saw two red light blinks and that indicated "Pressure switch stuck open". I replaced the pressure switch. Worked for about 2 hours then just stopped. I happened to be up there when it stopped and noticed 4 red blinks "High aux or spill limit switch open." Here's the strange thing. It will run for at most 2 hours then just stop. If I climb up in the attic and hit the cover, it kicks back on, sometimes for 5 minutes, sometimes for an hour. I was in the process of removing the cover one time and it kicked on. Not sure what else to try. Thanks.

Update: Just realized heater wasn't working again so I climbed back up in the attic. I sat down in front of the unit and it immediately clicked on. Almost seems like a short somewhere that is affected by the slightest movement.

 

[Focused2]

I would look at the fitting and hose related to "proving" the switch. Says you cleaned it , but any small obstruction can keep the switch from "making" (closing).

 

[jason92s]

I would look at the fitting and hose related to "proving" the switch. Says you cleaned it , but any small obstruction can keep the switch from "making" (closing).

Thanks for your reply. I took that apart after putting the new pressure switch on. I was up there earlier. It shut off a few minutes earlier so I knocked on the panel door very lightly and it started right up. 3 minutes later it shut down. I waited a few seconds and knocked on the panel again. Started back up and ran for about an hour (not an hour non-stop) before shutting down.

 

[bausin]

How about taking off the door, taping the door switch closed, and poking around with a stick until you find what makes the furnace restart?