I am going to call furnace companies tomorrow, but its worked for 4 years no issue. Used it a few months ago no issue, turned right on from thermostat/nest. Today I realized it wasn't firing up when I called for heat, I hear it like priming/but no ignite then turns off. I took the cover off the panel, vacuumed it out, looking at it. Tried it again, fires right up. Runs like a champ! Put the cover on, thinking I fixed it somehow. It won't turn on, ok. annoying, I repeated by taking cover off, fires up. I put the cover on, nogo. I loosen 1 screw. Just a hair, where a small gap opened, and she fires up. So one little air crack in door being opened is letting furnace run properly. I googled and found out people say its a intake clog typically, not enough fresh air? I shop vaccd the intake tube, nothing came out. I put a new filter in for heck of it, nothing. Everywhere is closed today, and its not an emergency. But tomorrow before I make a bunch of calls im trying to figure out the best route of ideas. If the furnace runs fine, it has spark, and gas, but lacks the air. By opening the cover, it has air. Is this a faulty pressure gauge or some kind of gauge that determines the air? kind of perplexed. I was thinking its the igniter, but it ignites just fine when the cover is cracked/off. so I mean, that seems to work fine. Is there a sensor on the igniter that determines if theres enough air, or is that another sensor? This is what's on my furnace as igniter.