I have two problems with my gas force air furance (Armstrong Ultra 80 SX). The furnace is about 13 years old.

I had an inspection and cleaning done on it a few days ago. The tech said that it looked like the heat exchanger was rotting and that I needed to replace the furnace. The diagnoses was based on a small amount of flame back burn (not all of the flame going into the hole) and a light brown residue powder coming out of the joint of the exhaust pipe.

In the process of checking he neglected to remove a set of alligator clips from the control board (R and W). I did not realize this until I went to turn the heat on the next morning and found the burner off and the clips in place. I turned the burner on and removed the clips.

The fans started working but the burner would not light.

I brought another tech from the same company back. After checking all of the circuits and other parts. He found that when he disconnected the thermostat from the control board (by removing the R and W wires) the blowers would run constantly and the burner will not ignite.

He concluded the control board was bad.

My question is ... could leaving the alligator clips connected to the board overnight cause a short circuit of the control board?

I thought maybe the clips may have gotten jostles when the fans started or the door was closed to close the circuit to cause a short.

What do you think? Do you have any suggestions of other things to check?