My furnace gives me this code by flashing the led 4 times which reads on the diagram in it that the limit circuit is open- I cleaned then little buttons that I think are the sensors. The blower won't shut of and just blows cold air- the burners are not igniting when I turn the thermostat way up. Any suggestions?

Some limit switches are resetable. Push button until it clicks. Others have to be replaced.

Check for obstructions in the venting system.

The limit circuit is open because the unit probably overheated or was not firing properly/flue problem. Look on the wiring diagram on the back side of the blower door and see if you can find the item on the drawing.

The rollout limit is part number 026-34027-000

The limit switch is part number 026-34028-001

Well, here is what I have discovered! First, my ignighter was bad (had a gap where it had burnt apart and is on order for $25.00, not 77.00 the heating company wanted) and needs replacing. This is simple to do. The limit switch is to keep you furnace from burning the house down, These switches have a manual reset ( I took them out and played with them and put them back in and they worked). The limit swithc being open kept the furnace blower running and blowing cold air. So when the ignighter comes I should be good to go. Hope this helps the next person with the same problem. If the burners aren't going on check the ignighter, to make sure it glows when the heat is starting to turn on. That is number one, and you can easily take it out and inspect it for cracks like mine had. Sorry to answer my own question, but I feel pretty cool now. Hope it all works when I get the part.

The limit switch tripped for a reason and that reason was not the ignitor being cracked. It is highly unlikely the limit switch will prevent the house from burning down but you never know. What it really does is prevent the furnace especially the heat exchanger from sustaining damage that is unrepairable. That means you would have to replace the heat exchanger which is the heart of the furnace. Keep a very close eye on the unit if you get it running since the problem is not solved with the limit switch fault situation. Good luck.

I get 4 flashes on my DGU10014UB which says high limit open... the furnace ignites but the blower motor sounds like it is "loading up" and will not kick in. Then everything shuts down