Suburban SF30F Furnace Issue - Popback?

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OneMonthRV

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Joined
Mar 20, 2018
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Hi All,

My first time here with a problem.

I have a weird gas furnace issue in my RV I need advice on.

It's a propane powered Subrban SF30F furnace, probably from 2002.

It will be running fine, gas burner has lit and fan is blowing heat. Then there will be what sounds like a second gas lighting, like a little mini pop/explosion, and then it keeps running but the burner now sounds all rumbly and irregular, like it is not burning cleanly, or a bad air mixture.

It don't believe it is a mechanical issue like a fan. It sounds burner related. Looking it up it may be what they call popback, or something similar.

I have taken the furnace all apart, cleaned everything, and it all looks good.

I thought it might be a bad propane pressure regulator, but with a new one the same problem.

Really at a loss.

Suggestions?

Thanks.
 
That sounds like a secondary flame ignited and it's burning somewhere outside the burner chamber. That steals some of the gas flow and disrupts the air/fuel ratio at the main burner chamber. I'd look carefully at the gas inlet valve and tubing to the burner chamber, and also at the exhaust area. Also check the chamber walls for a crack or hole.  Seems like you would have noticed some evidence when you had it apart, though.
 
Thanks Gary. That is what I thought also. But I looked everything over carefully and could not find any issues. The gas inlet tube is solid, and I blew out the jet. No problems there. The burner itself looks good. And the heat exchanger does not appear to have any holes. I am stumped.

I was wondering if an old supply hose before it gets to the heater somewhere under the trailer could be an issue? Low pressure? Maybe a leak or clogged up hose? Most of it is run copper, but there is an old flexible hose up front. Some imbalance in fuel to air ration? I even wondered about low 12volt battery power, leading to low battery voltage, so lower air flow, allowing the issue. I have not tested for that but it seems to be blowing fine.
 
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