Flame rollout from bottom burner only


Old 10-09-15, 08:52 PM
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Flame rollout from bottom burner only

Hi all...

I have a two year old Ruud 120,000 BTU horizontal high efficiency furnace that
has been converted to propane. The furnace is oversized for the application.

There are six burners in a vertical row. I'm getting some gas rollout from the bottom burner only, which kicks out the flame limit switch located there. The top five burners are fine with clean blue flame. The tech who came out said I probably have a blocked heat exchanger tube and recommended that I have him replace the entire heat exchanger. EXPENSIVE!

I was told by someone else in the trade that I could just block off the bottom gas jet and thereby run the top five burners only. Since the furnace is oversized the lowered efficiency from one inactive tube shouldn't be a problem.

Does this sound OK?

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Old 10-09-15, 09:04 PM
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Welcome to the best DIY forum on the Internet.

Your answers are no and no. Looking at the second piece of advice first, all burners must be operational because the ignitor is at one end and the flame sensing device is at the other end of the burner string. If the burner in question is the one closest to the ignitor and you disable it then none of the burners will light. If it is at the end with the flame sensor then the safety shutdown system will activate shutting down all gas flow and all burners because it does not sense a flame.

Before replacing the heat exchanger it makes much more sense to clean the offending tube in the heat exchanger. If your tech doesn't know how to do this he shouldn't even be working in the trade. If the tube is too badly plugged to clean then rather than changing out the heat exchanger a whole new, properly sized, furnace should be installed.
Old 10-09-15, 09:05 PM
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Welcome to the forums.

Your problem begs the question.... why was that big of a furnace put in if it's over sized ?

I'm not an authority on gas problems but I wouldn't advocate blocking off one of the burners unless it was a factory authorized patch.
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