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I'm experiencing a situation on a job we just installed 2 new Navien NCB-240 Combi boilers (natural gas)
The customer was in the yard gardening and smelled gas so he called the gas co. They came out and confirmed there is a high level of natural gas being expelled out the exhaust pipe outside and he proceeded to red tag the units. I thought it was isolated to just 1 of the 2 units but on the 2nd time out he check both and they are both having the same issue. I was present the 2nd time out and witnessed his meter and it showed a 20% combustible gas reading.
I took my digital manometer and checked the gas pressure at the burner and my reading was 19"WC which I knew was extremely high. But it was possible as the area has high pressure gas mains and a step down regulator in the basement. I thought we had discovered a bad regulator and surely the cause of the problem until the gas co came back out to check the pressure just after the regulator and the reading was 8" WC. The customer sent a picture of the manometer showing 8"WC.
Has anyone experienced this before? Can you give any suggestions on what might be going on here with all this natural gas coming out the flue??
I did have the local Navien rep out to see if he could help but he only came to check the settings, dip switches and visually inspected the flame. He explained to me that some raw gas will be present in the exhaust especially during pre and post purging. He also went on to say that there also is some unburned gas always in the exhaust because the units are not 100% efficient. He said but the correct way to check it is during "high fire". He said that you never really have this call because all the old exhaust with the gas in it went up the chimney now it's going out thru the side wall where it can be smelled. I'm no gas expert but this just sounds a bit absurd, what he telling me is that if you have an 81% efficient burner the 19% of the gas is not being burned goes out the chimney?? Or in our case the 93% eff burner will expel 7% raw gas out the flue pipe? I don't believe what I'm hearing, this would be an explosion hazard if someone was out smoking in the garden... Can anyone elaborate on this so I can understand more about the combustion process.
Back to the issue we have a 20% natural gas or "combustible gas" reading coming out of our exhaust and rightfully so a customer that is quite upset.
Any feedback would be helpful