Tips for adjusting air/gas combustion mix in Navien CH-240

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Joe B

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Hi,
I have moved into a house with a ten year old Navien CH-240. It has one of those "two-in-one" intake exhaust things, and it runs about twelve feet out the side wall of the garage to the outdoors. (The Navien unit is in the garage.)

I have always noticed a gas smell from the exhaust when it runs, often noticeable from many feet away. I read that a little gas smell was normal, so I put it out of mind. But I just decided to have the gas company out to measure it, just to be sure.

With the Navien unit running while a hot water tap is fully on, the exhaust is blowing out 90% LEL gas and 121ppm CO.

This CH-240 unit does not have some of the altitude-adjusting DIP switches that the newer units have. Has anyone else here had a similar issue with their Navien? Did you have a tech adjust some kind of air/fuel mix in these units? Do you have any tips for successfully troubleshooting and/or adjusting the air/gas mix?

I am hesitant to adjust anything since these units seem so emotionally sensitive!
 

John Gayewski

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Hi,
I have moved into a house with a ten year old Navien CH-240. It has one of those "two-in-one" intake exhaust things, and it runs about twelve feet out the side wall of the garage to the outdoors. (The Navien unit is in the garage.)

I have always noticed a gas smell from the exhaust when it runs, often noticeable from many feet away. I read that a little gas smell was normal, so I put it out of mind. But I just decided to have the gas company out to measure it, just to be sure.

With the Navien unit running while a hot water tap is fully on, the exhaust is blowing out 90% LEL gas and 121ppm CO.

This CH-240 unit does not have some of the altitude-adjusting DIP switches that the newer units have. Has anyone else here had a similar issue with their Navien? Did you have a tech adjust some kind of air/fuel mix in these units? Do you have any tips for successfully troubleshooting and/or adjusting the air/gas mix?

I am hesitant to adjust anything since these units seem so emotionally sensitive!
Yeah don't adjust it. Let a tech do it.
 

Joe B

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An update, and a new question.

Had a skilled boiler tech check and adjust combustion. He spent all day with the Navien, including replacing many O-Rings, doing a flush, replacing the igniter and fan flapper valve.

Before the adjustment, low and high fire.
IMG_1787 2.jpeg
IMG_1788 2.jpeg


After the adjustment, low and high fire.

IMG_1793.jpeg
IMG_1794.jpeg


Then, had the gas company come out and do a reading on the exhaust. It is now 3 - 12% LEL & CO 100 - 120ppm (was 90% LEL gas and 121ppm CO). However, gas company says this is still too high, to be suspicious of the air/gas mix for combustion, and the exhaust still smells strongly of gas.

But I noticed something. 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.

venting dip switches copy.png


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?

Thanks for any tips.
 
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