I hava a Trane XL90 furnace that was installed new about 3 years ago (oct 2006). Yesterday it stopped heating; and only blows unheated air out the registers. The Control board Red LED flashes a code 5. The Green LED is flashing slowly. The local HVAC company looked at it and concluded that the Control board was bad. It's kind of expensive to replace the Control board and so is there a way to confirm that is the problem?

The info for the codes should be on the back of the door or on the control itslef. Also in you owners manual. The furnace has a 5 yr warranty so the board should not cost a thing.

Thanks for the info -- I didn't know the codes were there and my HVAC guy was less than clear on the warranty question.

I believe the problem has been solved. I cleaned/remade all the ground connections because I heard this furnace (Trane XL90) is very sensitive to any faulty ground connections. The unit now fires up properly -- No more fault codes. Cycled repeatedly and works every time, but I'll keep an eye on it for a few days.