Greetings:
I am hoping someone can offer me some assistance here. I have a customer that has a standing pilot Trane furnace. Some time ago it started failing to light the last burner once the heat exchanger was hot. The flame will come within about an 1 1/2 inches of the burner on the spreader. Of course, after a short period there will be a small explosion and the burner may light. This only happens when the exchanger is hot, it will work normally when it is cold, and don't happen all the time.
I replaced the burner assbly, gas valve, adjusted the manifold pressure above 3.5" and below, I adjusted the air up and down and yet the problem still presists. I think I could solve the problem by moving the pilot to the center or restricting the air flowing to the burner, but I don't want to modify the furnace. I am more interested in finding the solution. I'm sure it is something simple that I am overlooking. One thing I haven't done yet was check the reaction time or flow differences between the Honeywell gas valves and WR that normally comes with the furnace.
If anyone can help me I will greatly appreciated it and so will my customer.
Thanks in advance