I have an Armstrong Air Ultra sx 80 model# GUJ075D10-2B. The furnace has satisfied the call for heat and everything has shut off and waiting for the next call. The problem is on the start-up. When the igniter starts the flame, it is like there is a small build up of gas in the heat exchanger and it ignites. It will create a loud "thump" in the furnace. Is this caused by a small amount of leaking gas, and if so , how can it be fixed?

You have a bad light off situation. You may try cleaning the burners and especially the flame jumper area. Is the situation persists I highly suggest you contact your local HVAC company for the repair since the gas pressure entering the unit may be to high for some reason or another.

Thanks hvac 1000. That gives me a starting point. Trying not to get my wallet tapped too hard. If the cleaning doesn't work than I will have to call a tech. to come out to check the gas pressure. Thanks again. Jim

I hope you get it going it seems $$$ is a bit short right now for many people.

When I have to replace this thing, what brand unit would you recommend as being best quality and warranty for price? Can you give me an opinion?

All furnaces are designed to operate it is the install that makes the big difference. Get the best installer with the most experience. See article below.

That's what I was finding out as I was looking into it. All the top brands are about the same. Excellent worksheet. Thanks again.

Good luck with your decission.