Wanted to know if anyone could help me troubleshoot this problem..
This furnace will not fire up (every now and then), basically what happens is the igniter lights up, but will shut down after 5 seconds or so. It will do this three times until it goes into lock down, code 34 flashes. I reset power to the unit and it will fire right up no problem. Unit locks out "every now and then", but will restart and fire up as soon as I reset the power to the unit (turning the emergency switch on and off). Followed the troubleshooting guide to no avail. Unit does this once a day, once every other day, once a week, very sporadic, but fires right up after resetting the power. Any suggestions? Thanks.

You may be having a problem with a pressure switch breaking the control circuit during the startup causing it to try and restart until it goes into lockout.Check the tube on the pressure switch and make sure the fitting that the tube is connected to is clear and unobstructed, chech for loose wire connections also, good luck, Mike

I have had this same problem. I cleaned the flame sensor. The ignitor is working. But still a couple of times a day and first thing in the morning it will not ignite.

I noticed that when it tries to light it would only light a couple of the burners.

The "Cross-overs" (Slots on the end of the burners) are clogged with dust or residue. So, remove the burners and clean them out. Be careful not to break the ignitor, you may just want to take it out before doing this. I had five burners in my furnace. The burners are the silver tubes where the flame comes out. I just flushed mine out with water and then dried them. Now, my burners light on the first try every time. This is easy to do and will most likely fix your problem.