Navien CH-240 DIP Switch 4 and combustion

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Joe B

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I have been troubleshooting the gas smell at the exhaust of my Navien CH-240.

I noticed that DIP switch 4, which should be ON for and individual vent, and OFF for a shared cascading common, is set to OFF. I have a concentric intake/exhaust, and not a shared cascade common, which is for multiple daisy-chained units.

View attachment 86130

Is it ok to flip DIP switch 4 to ON? Will this have any affect on combustion and possibly reduce the gas smell at the exhaust?

I don't want to flip it it might negatively affect combustion or go wonky on me. Thanks for any tips.
 

breplum

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Flipping switch 4 to ON will be the right thing to do.

It is not terribly unusual to smell a little uncombusted gas at the vent terminus at the very beginning of ignition, but, not continual.
 

Joe B

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Hmmm... I do indeed smell gas at the exhaust the entire time the unit is running. I am not certain that combustion can be dialed in better by my tech.

Will flipping switch 4 to ON change the combustion air/gas mix too much? I don't want to do something that causes a new problem. Especially since that switch has been OFF for ten years.

Thanks for any insight.
 

Fitter30

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When has the heater been looked at? Burner analyzer been used. Did u check the air inlet filter right inside of the cabinet at air inlet pipe.
 

Joe B

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@Fitter30 Just this past year. Burner analysis here. The air inlet filter is, and always has been, clean.

I am also going to run a cheap endoscope from the concentric exhaust/intake to check for air intake blockages.
 

Joe B

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Where are u smelling the gas and when ( like ignition)
The gas smells from the exhaust, which runs through the garage, is a concentric intake/exhaust type, and exits through the wall of the garage. Run is about eight feet.

The gas smells continuously while the unit is running. If the unit is running, and is exhausting, there is a gas smell at the exhaust.

Absolutely no problems inside.
 

Fitter30

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Burner needs to be pulled and inspected. As well as the heat exchanger. Then flue gas analyzer used to set up the burner. Probably have a high Co reading.
 
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