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HTP Phoenix light duty combustion ?'s
So I had one of these put in about a month ago and it's always had a woosh sound when it fired up. Not loud or anything but noticeable. After a week or so I switched it to eco mode because I couldn't make the thing run out of hot water if I tried. It recovers insanely fast. It started making that foghorn noise when in eco mode. Only for the first 15 seconds or so after firing and then it quit. So I talked to the guy who installed it and he said put it back to regular mode and he'd call me when he could stop by. I'm still waiting for that call...
So being the handy guy I am I started reading. And reading and reading and reading... These gas valves are quite sensitive from many posts I've read. I got frustrated with all the posts about flex pipe and regulators causing these issues. Decided to get rid of the flex and hard pipe it myself since this was one of those "favor" installs. I also found a shut off valve with a really small opening that seemed restrictive so I replaced that with a full port ball valve as well. It definitely changed the sound of startup and operation but something still isn't right.
I used an analyzer and a manometer to check the flue mix and gas pressures. I see 9.7% CO2 at high fire and 9% at low fire, both below 20ppm CO. Those numbers seem great to me (based on my hours and hours of research). The thing I'm confused on is the low fire mode. High fire has a nice, sweet looking blue flame. Low fire get much more yellowish. I know color doesn't mean everything but I'm looking for an answer on why that would happen. Also am I the only one with a sight glass right behind the gas valve? It's almost impossible to see anything where it's placed.